Tengen was part of Atari, formed around 1988. They had an official license from Nintendo for about a year--in that time they had produced Gauntlet, R.B.I. Beseball, and Pac Man.
The relationship between Nintendo and Tengen got a little rocky during the Christmas season, for there was a shortage of roms and Nintendo told Tengen that it was "to bad" if they only recieved half the aount of promised roms for the season.
As any smart company would do, Tengen designed their own way to break through the NES's lockout chip, allowing themselves to produce unlicensed games.
Tengen was sued by Nintendo over a variety of things, such as Tengen's key to breaking the lockout chip. Those lawsuits ocuredin the 88-89 time period. Tengen also had a lawsuit over their Tetris, the better of the two Tetris games I must say.
Around 1990, Tengen started loosing it's fizz due to paying off their court costs. I believe Tengen stopped making unlicensed games in 1993.
But what kept Tengen from going out even after getting sued twice, and being unlicensed? Tengen had a fairly good position in the market. They had the same advantage Codemasters had: a wide range of popular games. People played all these great games in arcades, such as Ms. Pac Man, Toobin, and Super Sprint. That is what Tengen had going for them. Quality.
Released Games Unreleased Games
After Burner Airball
Alien Syndrome Cyberball
Fantasy Zone Licensed to Kill
Gauntlet Police Academy
Indiana Jones Temple of Doom Xybots
Klax
Ms. Pacman
Pac Man
Pac Mania
RBI Baseball
RBI Baseball 2
RBI Baseball 3
Road Runner
Rolling Thunder
Shinobi
Skull & Crossbones
Super Sprint
Tetris
Toobin
Vindicators