As the years progressed, Tetris jumped from platform to platform. The Gameboy edition was hugely popular, followed by editions for increasingly sophisticated systems as well as graphing calculators and other simpler devices. SNES begat Gamecube, which led to PS3. The game also expanded to new categories. As of April 2011, EA — which purchased the worldwide mobile rights in 2005 — had seen Tetris bought 132 million times, making it one of the best-selling mobile games ever. For comparison, the free, ad-supported version of Angry Birds boasted 140 million downloads by August 2011.

The sustained success of such a simple game surprised almost everyone. "I've been at this since 1989, and everybody back then thought it was going to be a dead issue by 1995. It was anything but a dead issue by 1995. It was a huge issue by 1995. It's gone on to become the biggest issue on mobile phones," Rogers says. "There are a couple of ways of looking at that. One is that in its simplicity, it hits a nerve that other games don't because they are more complicated. The other way of looking at it is that we've done a pretty good job keeping it alive by adding bells and whistles over the years to keep it relevant."

One essential development occurred very early. Rogers says Pajitnov's original game revolved around the number of Tetriminoes a user could play rather than clearing lines. The first version Rogers helped design included bonus points for clearing two, three, and four lines — known as a Tetris — at once, a change that fundamentally altered the game forever. Later editions added moves such as twists like T-Spins and L-Spins that allowed gamers to maneuver in tight spaces and earn more points for doing so. (See sidebar for other variations.)

The latest in the long line of innovations is the one-touch system. The Tetris Pajitnov invented required seven buttons: left, right, rotate left, rotate right, hard drop, soft drop, and hold. That system doesn't translate to touchscreens, nor would it work for the mouse-based game that Blue Planet's engineers envisioned for Facebook. So the company developed Tetris Stars for Facebook and worked with EA to create Tetris One-Touch for mobile devices ($.99 for iPhone) and tablets ($6.99 for iPad). When they were building the games, the discussion centered around how much to change the core game. The answer: as little as possible.

"There was some back and forth during the design of whether we were going to focus on multitouch to let players use two fingers to pinch or rotate. We decided not to support multitouch because that would eliminate compatibility with mouse-based games. We iterated on a number of different prototypes before we ended up with the one-touch," Jared Eden, a Tetris Stars producer, says. "You go out and try all sorts of different things. Some are really complex, and as you're iterating, you distill down to the most basic, pure essence of the design to something so simple. That's where we ended up, and we're really happy with it."

The key to the one-touch solution is the AI. It offers the player a few choices for piece placement, and he picks one by touching or clicking the on-screen silhouette. (If the player waits too long, the Tetrimino falls straight down.) As with regular Tetris, the speed of the game increases as the player clears more lines and levels up. The AI is not perfect—a player can get a new set of choices by clicking or touching elsewhere—but it provides a new playing experience that works well on a touchscreen or Facebook.

"You have to move a block over three rows, rotate it, then drop it, and do that in a matter of seconds. You can't do that on a touch device. It's impossible."

Indie gamemaker Zach Gage, who admits he's never loved Tetris but respects the game, thinks Eden and the Blue Planet crew made a smart decision when updating the game for touchscreens. "The difficulty of Tetris is when it gets fast and you have to make these mechanical motions. You have to move a block over three rows, rotate it, then drop it, and do that in a matter of seconds. You can't do that on a touch device. It's impossible," he says. "I think that's why they were smart. They looked at it and said, 'This is impossible. We're going to have to change it, so let's make the minimum number of changes that we need to make to completely change it from that mechanical aspect. We need to make people interact with it.'"

Gage's thoughts are accurate: Tetris Stars and EA's One-Touch are elegant solutions for the masses. (The mobile version also features Marathon mode, which plays much more like traditional Tetris and fails for the mechanical reasons Gage describes, as well as Galaxy mode, which requires player to perform challenges for coins. The rewards are similar the gamification elements on TetrisFriends.com, an online repository where players earn ranks, rewards, tokens, and stars.) The huge number of paid downloads indicate that it found a large audience. which was exactly the intention of the gamemakers. "We need to reach out to the casual gamer market that has gone the way of the casual gamer," Rogers says. "That's where the market is and we have to shape that market." One-touch Tetris achieves this goal. But in attempting to attract the casual market, did Rogers and Blue Planet go too far?