Created by Alexey Pajitnov in 1984. The Game Boy version was released in 1989 from Nintendo R&D1. Received for 6th birthday along with Super Mario Land. This stuck with me a long time - I played Tetris regularly for years, all the way through Jr. High, until I had actually maxed out the game's speed/level count and continued into infinite play. At that point my interest dropped off, but I can say this game has given me as much entertainment as any game ever.
I've also lost count of the different versions of this that I've played. At least includes:
I've even reimplemented it myself (as a learning exercise - definitely lost this).