Defender was Williams Electronics' first attempt at developing a new video game; the company's earlier game was a Pong clone. The popularity of coin operated arcade games in 1979 spurred the company to shift its focus from pinball games to arcade games. The company chose Eugene Jarvis, who had a successful record of Williams pinball games, to head development.Larry DeMar, Sam Dicker, and Paul Dussault assisted Jarvis. At the time, Williams had a small staff and the management was unfamiliar with technology used for its electronic games. As a result, the staff was afforded a large amount of creative freedom.

Initial development

Space was a popular setting for video games at the time, and Jarvis felt the abstract setting would help obscure simple graphics that lacked realism. Initially, Jarvis spent 3–4 months developing color variations of Taito's Space Invaders and Atari's Asteroids. First inspired by Space Invaders, he created a similar game with new gameplay mechanics. After spending a few weeks on the design, however, the team abandoned the idea, believing it lacked enjoyment. Development then shifted to emulating Atari's Asteroids, but hardware differences between Asteroids and Defender's proposed specifications were problematic. Asteroids displays vector graphics on a special monitor, while the staff planned to use pixel graphics on a conventional monitor. The team experimented with recreating the game with pixel graphics, but also abandoned it because they felt the gameplay lacked enjoyment and visual appeal.

Believing their first attempts to be too derivative, the developers held brain storming sessions. During a session, they agreed that one of Asteroids's favorable elements was its wrapping effect. They felt a game that allowed the player to fly off the screen would be exciting, and decided to create a game world larger than the screen displayed. The game's environment was made longer than the screen, with the visible area scrolling horizontally. Expanding on the idea, they envisioned a version of Space Invaders rotated 90 degrees. By changing the orientation of Space Invaders' design, the ship moved up and down while flying horizontally. Large asteroids, an element from Asteroids, were then added to the game world, but were later removed because the staff felt it lacked enjoyment. Jarvis intended the screen to only scroll from left to right; fellow Williams employee Steve Ritchie, however, convinced him the game should be able to scroll in either direction.

After six months of development, the team felt the game had not made enough progress. They examined other games and concluded that survival was a necessary component to implement. To achieve this, they devised enemies to present a threat, the first of which was the "Lander". Jarvis enjoyed violent, action entertainment, and wanted the game to have those elements. However, he felt the action should have a reasonable objective. Inspired by the 1960s television show The Defenders, Jarvis titled the game Defender, reasoning that the title helped justify the violence. He added astronauts to expand on the space theme and give players something to defend while they shot enemies. The element of flying over a planetscape was added after a brainstorming session between Jarvis and Ritchie. The landscape is depicted as a line only a pixel wide, primarily because the hardware was not powerful enough to generate anything more detailed.

Later development

By July, development was behind schedule and Jarvis's superior began to pressure him to finish the game in time for an upcoming trade show, the AMOA, in September. Jarvis spent several weeks creating the astronauts, which his boss felt should be omitted if the process didn't speed up. The pressure frustrated him to the point he considered resigning. Around that time, a new programmer named Sam Dicker was hired. He assisted programming the game and added visual and audio effects. For example, Dicker implemented a particle effect algorithm to generate unique explosions for destroyed enemies. The new elements re-invigorated Jarvis, who felt the project began to show promise.

Development then shifted focus to the enemies. Landers were given the ability to capture humans, and a new enemy was devised from the mechanic: "Mutants", Landers that successfully abduct an astronaut. The Mutants added a rescue element to the game that Jarvis believed made it more interesting to players and encouraged them to continue playing. The element of making a "comeback" from a dire situation was applied to the planet as well. Jarvis felt it mimicked the ups and downs of real life. "Bombers", enemies which release floating bombs on the screen, were added next. More enemies were added to create different gameplay elements. "Swarmers" and "Pods" were designed to attack the spaceship as opposed to the astronauts. "Baiters" were included to add pressure to the player by preventing them from lingering. The enemies quickly follow the spaceship to collide with it, and were based on a similar enemy in Asteroids.

By September, the game was still unfinished, and almost every Williams programmer assisted in meeting the deadline for the AMOA trade show. The evening before the trade show, the arcade cabinets were delivered for display. The developers, however, forgot to create an attract mode—an automated sequence designed to entice an audience to play—for the game, and began working on it that night. Early the next morning, the team created the final EPROM chips for the mode and installed them in cabinets. The chips, however, did not work and the designers made additional attempts to correct the problem. Once the attract mode was operational, Jarvis and the team returned to their homes to prepare for the show. After the show, the developers expanded the game to allow users to play indefinitely. The display model featured five levels, which the team felt was more than enough because of the game's difficulty. Most Williams employees could not progress past the third level and Jarvis's score of 60,000 points seemed unbeatable to them. The developers decided it was best to be prepared for players that might exceed their expectations and added more levels that repeated.

Hardware

The game features amplified monaural sound and pixel graphics on a CRT monitor. A Motorola 6809 central processing unit handles the graphics and gameplay, while a Motorola 6800 microprocessor handles the audio. A pack of three AA batteries provide power to save the game's settings and high scores when the machine is unplugged from an electrical outlet. The cabinet artwork is stenciled on the wooden frame.

Development started by focusing on the game's hardware. The staff first debated what type of monitor to use: black and white or color. They reasoned that using advanced technology would better establish them as good designers and chose a color monitor. The developers estimated that the game would require 4 colors, but instead chose hardware that could display each pixel in 16 colors. At the time, the designers believed that was more than they would ever need for a game. The monitor's resolution is 320×256, an expansion from the then industry standard of 256×256. The staff believed that the wider screen provided a better aspect ratio and would improve the game's presentation. Video games at the time relied on hardware to animate graphics, but the developers decided to use software to handle animation and programmed the game in assembly language. The switch allowed them to display more on-screen objects at a lower cost.

The game's control scheme uses a two-way joystick and five buttons. Jarvis designed the controls to emulate both Space Invaders and Asteroids simultaneously. The player's left hand manipulates the joystick similar to Space Invaders and the right hand pushes buttons similar to Asteroids. The button functions also use a similar layout to Asteroids's, with the button to shoot projectiles and accelerate on the far right and left, respectively. Jarvis reasoned that players were accustomed to the control schemes of past games, and felt altering past designs would prove difficult for them.

Initially, the game slowly gained popularity.Defender did not attract much attention at the 1980 AMOA show. In retrospect, Jarvis believed many passersby were intimidated by its complexity. The game, however, was well received in arcades, and crowds gathered around the cabinet during its first nights of play testing. The success spurred Williams to release a cocktail version as well.Defender eventually became Williams' best selling arcade game, with over 55,000 units sold worldwide. By 2004, the game was a popular collector's item; the upright cabinets were common, while the cocktail models were more rare. Since its release, it has become one of the highest grossing arcade games ever, earning over US$1 billion. Williams employee Larry Demar was surprised at the game's popularity, stating that it was the only game he'd seen able to earn that quantity of quarters. Six months after its release, the game was one of the top earners in the United States video game industry. Mark Stearny of JoyStik magazine called Defender the most successful game in 1981, commenting that it outperformed Pac-Man.

The game garnered praise for its graphics, audio, and gameplay features. Gamespy's David Cuciz lauded Defender's challenging gameplay, commenting that it is representative of what other games should be. He described the graphics as "beautiful", citing the varied sprites and flashing explosions. Matt Barton and Bill Loguidice of Gamasutra stated the audio-visuals and gameplay's depth balanced the excessive difficulty. They praised the game's "catch and rescue" feature, as well as the minimap. Cuciz also praised the minimap, stating that the game is impossible without it and that it allows players to plan strategies. Author John Sellers praised the audio-visuals and the connection between the game's plot and gameplay. At the time of its release, Stan Jarocki, director of marketing at then competitor Midway Manufacturing, described the game as "amazing". In 2008, Guinness World Records listed it as the number six arcade game in technical, creative, and cultural impact. That same year, Retro Gamer rated the game number ten on their list of "Top 25 Arcade Games", citing it as a technical achievement and a difficult title with addictive gameplay. Also in 2008, Edge ranked Defender the sixth best game from the 1980s. The editors described its design as very "elegant" despite a lack of narrative and characters.

Defender is often described as one of the most difficult games in the industry. GameDaily rated Defender the ninth most difficult game, citing the attack and rescue gameplay. Author Steven L. Kent called it "one of the toughest games in arcade history". He also stated that novice players typically are able to play only a few seconds, and that enthusiasts saw proficiency at the game as a "badge of honor".David Cuciz echoed similar comments. Sellers described Defender's difficulty as "humbling", saying that few could play it with proficiency. He further stated, however, that players would continue to play despite the difficulty. Author David Ellis attributes the game's success to its challenging design. Its difficulty is often attributed to its complex control scheme.Edge magazine called Defender "one of the most difficult-to-master" games, describing its controls as "daunting".Retro Gamer editor Craig Grannell called the game and controls "ruthless" and "complex" respectively.

Players have competed to obtain the highest score at the game and the longest play time on a quarter. Competitive playing for the longest play time was popularized by Steve Juraszek from Illinois, who played Defender for over 16 and half hours in 1982. Though the authenticity of the record was questioned, the media attention spurred other players to attempt the same feat. Expert players exploited software bugs to extend the length of their play time. One bug, related to how the game keeps track of scoring, allows players earn a large number of "extra lives". Players can then use the extra lives to leave the game unattended while they rest. Other bugs allow the ship to avoid damage from the enemies, also prolonging the length of play.

The game has been referenced in music: Manilla Road's song "Defender" on their 1982 album Metal, Buckner & Garcia's song "The Defender" on their 1982 album Pac-Man Fever, and the Beastie Boys' song "Body Movin'" on their 1998 album Hello Nasty.

Professor Jim Whitehead listed Defender as the first horizontally scrolling shooting game, and describes it as a breakthrough title for its use of full 2D motion, multiple goals, and complex gameplay that provides players with several methods to play. James Hague of Dadgum Games called Defender a landmark title from the 1980s, and credits it as the first horizontally scrolling game. Stearny said that the game's use of scrolling helped remove design limitations associated with the screen. Cuciz stated that Defender's use of scrolling introduce the "first true 'gaming environment'". He further said that though the game's minimap feature had been introduced before, Defender integrated it into the gameplay in a more essential manner. Stearny described it as the most important space game in the early 1980s. He commented that its realism and technological advances pushed developers to create more popular games, citing Gorf and Phoenix as examples. Vince listed the game as a classic title that introduced new technology, specifically scrolling. Ellis stated that prior to Defender, companies designed video games to have a balanced challenge. They believed games should be easy enough to attract players, but difficult enough to limit play time to a few minutes; anything too challenging would dissuade players. Loguidice and Barton commented that Defender's success, along with Robotron: 2084, illustrated that video game enthusiasts were ready for more difficult games, which spurred developers to create more complex game designs.

Jarvis's contributions to the game's development are often cited among his accolades. Author John Vince considered him as one of the originators of "high-action" and "reflex-based" arcade games, citing Defender's gameplay among other games designed by Jarvis. Ellis stated that Jarvis established himself as an early "hard-core" designer with Defender. In 2007, IGN listed Eugene Jarvis as a top game designer whose titles (Defender, Robotron: 2084, and Smash TV) have influenced the video game industry. Barton and Loguidice stated that the game helped establish Williams and Jarvis as key figures in the arcade game industry. Sellers echoed similar comments. After the success of Defender, Williams expanded their business by building a new facility and hired more employees. Before the expansion, Jarvis could work in isolation. But the influx of people created an environment he was unhappy with. He left Williams along with DeMar to found their own development company, Vid Kidz. The company served as a consulting firm to Williams and developed two games for them.

Remakes and sequels

The game was followed by several sequels that feature a similar design, but with elements altered and added. The success of Defender prompted Williams to release another game. The company approached Vid Kidz, who originally wanted to create a new game. DeMar, however, suggested creating an enhanced version of Defender to meet Williams' four-month deadline. Vid Kidz titled the game Stargate, and developed it as a sequel to Defender. It features new elements and improved the original's performance. Home ports of Stargate were released under the title Defender II for trademark purposes. In 1991, Midway released the arcade game Strike Force. It features gameplay similar to Defender, but with additional options and more contemporary visuals. Jarvis and DeMar assisted with the game, which was programmed by Todd Allen and Eric Pribyl. Subsequent sequels were released on home and handheld consoles: the 1995 Defender 2000 and the 2002 Defender. The 2002 release features three-dimensional (3D) graphics and behind the ship view opposed to the 2D side view.

Several home console and computer games like Defense Command, Repton, Dropzone, and Protector II copied Defender's design, while other built upon it. For example, Bob Whitehead's Chopper Command for the Atari 2600 and Dan Gorlin's Choplifter for the Apple II mimics Defender's gameplay and features. Video game designer Jeff Minter based several of his games on Defender's design. Magazines Edge and Retro Gamer commented that most official and unofficial ports failed to accurately emulate the arcade's gameplay, citing Planetoid, an unofficial version for the BBC Micro and Acorn Electron published by Acornsoft, as the only home version to succeed. Grannell commented that even fairly accurate home conversion like the Commodore 64 port lacked the arcade's polish. Versions like the Atari 2600 port distinctly changed the gameplay and graphics to comply with the system's specifications. Barton and Loguidice commented that the Atari 2600 version, along with Space Invaders and Asteroids, helped the system gain a dominant market share.

The success of the arcade game prompted Williams to release a pinball version in 1982. The pinball game features many elements from the original game: sound effects, enemies, waves, and weapons. One feature meant to emulate the reverse function of the arcade was a forerunner of the outlane "kickback" function found in contemporary pinball games. Williams produced less than 400 units, which have become rare machines.

In 2000, a web-based version of Defender, along with nine other classic arcade games, was published on Shockwave.com. Four years later, Midway Games also launched a website featuring the Shockwave versions. The game has been included in several multi-platform compilations: the 1996 Williams Arcade's Greatest Hits, the 2000 Midway's Greatest Arcade Hits, and the 2003 Midway Arcade Treasures.

In the late winter of 2012, Doug Mahugh (Joystik magazine) published his 30 year old Defender Strategy Guide. The manual was proofed by both Larry DeMar and Eugene Jarvis. Doug was the top master player of the day. On January 24th, 1982 played a marathon game for 24hrs as a response to Steve Juraszek's 16hr game featured in Time magazine.

• Datastorm, a similar game for the Amiga released in 1989
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