After Jarvis left to form his own company -- Vid Kidz -- with Larry DeMarthe, the two continued to design games for Williams, starting with Defender's 1981 arcade sequel, Stargate, which, for trademark purposes, became Defender II in later home releases.

Never reaching anywhere near the popularity of Defender, Stargate added new enemy ships, equipped the Defender with a limited-use invisibility (cloaking) device (a sixth button!), added two special stages after every fifth and tenth board, respectively.

It featured the titular Stargates, which among other things, transported the Defender to any humanoid in trouble and, under the right circumstances, allowed especially skilled players to jump ahead several levels.

This ability to jump made the game even more frenzied, and the best players felt it let them get one up on the game.

When asked about the inspiration for the game's Stargates, DeMar said the two "wanted something that would give some new appeal to the game [Defender], but that wouldn't be playable by the good players on Defender."

So the two "worked hard to develop a mechanism that would be good for the experienced Defender player, but wouldn't make them stay there for a long time."[6]

Screenshot from the arcade version of Stargate, which became known as Defender II for most home conversions.

Atari's 1984 conversion of Defender II, née Stargate, was a marked improvement over their earlier conversion of Defender.

A final -- though less direct -- arcade sequel, Strike Force, was released in 1991 through Midway to little fanfare.[7] While Jarvis and DeMar were on the staff, the game's main programming was handled by Todd Allen and Eric Pribyl. According to MAME's history file on the game, [8]

"Strike Force again has the player flying a spaceship over the surface of a series of two-way, horizontally scrolling planets, destroying enemy waves and rescuing humans from the alien invaders; with rescued humans hanging from the underside of the player's ship. Once these tasks have been completed, the mothership arrives to pick up the player's ship, together with any humans they have rescued. Players can decide which planets to attack, when to purchase additional firepower and when to attack the Apocalypse. Strike Force's graphics differ from the minimalist, stylish appearance of the first two games in the series; with full color sprites, multilayer scrolling and colourful, visceral explosions giving the game its own distinctive look and feel."[9]

Screenshot from the arcade version of Strike Force.

Besides the official home ports of the arcade games and the aforementioned Revenge of Defender, the Defender series would receive two more new official home entries: Defender 2000 (1995) and Defender (2002), as well as a 2006 release of the original arcade game on Xbox Live Arcade for the Microsoft Xbox 360, which added online options and a mode with sound and visual enhancements.

Defender 2000 from Llamasoft, published on cartridge by Atari for the Atari Jaguar, features a choice of three modes: Defender Classic (original arcade version), Defender Plus (audiovisual enhancement of the original with the option for helper droids to make the game a bit easier), or Defender 2000 (additional enhancements, including powerups).

The 2002 release of Defender for the Microsoft Xbox, Nintendo GameCube, and Sony PlayStation 2, took the series into 3D with a third-person, behind-the-ship perspective, creating a very different experience than its namesake. The Nintendo Game Boy Advance version retained the original's 2D perspective and included an option to play the original game, which some contemporary reviews indicated was the cartridge's saving grace.

Defender 2000 was one of several updates of classic arcade games on Atari's Jaguar console. Box back shown.

Although the series has long been surpassed in popularity in the modern niche of the shoot-'em-up genre, it was early games like Defender and each new generation of consoles that finally proved gamer adaptability to increasingly complex control schemes.

Of course, it can be argued that this complexity reached a point of diminishing returns and that's why more casual games and systems like the Nintendo Wii have proven so popular in recent years. Certainly, Bushnell's experiences with Computer Space and Pong (see the bonus chapters on Pong and Spacewar!) suggested that complexity was as bad as simplicity was good.

Nevertheless, Defender successfully challenged the idea that gamers couldn't handle or wouldn't play complex and difficult games in the arcade, awakening other developers to new, more sophisticated design possibilities.

[6] From the multimedia retrospective on Williams Arcade Classics (Midway, 1995; PC, Sony PlayStation, and others).

[7] In 1988, Williams, operating as WMS Industries, acquired Bally/Midway, and now operates under WMS as Midway Games.

[8] MAME stands for Multiple Arcade Machine Emulator. According to the MAME Documentation Project Website, "Its purpose is to document the inner workings of those pioneering games of the video arcade era. Remember Pacman, Space Invaders, DigDug, etc., well, they are all documented and what's more fully playable in the MAME project. You see, these arcade machines will not last forever, so the emulator and ROM Images are here to preserve these games."

[9] http://www.mameworld.net/maws/romset/strkforc.