Computer game Tetris celebrates 25 years
The game was created by Alexey Pajitnov, a computer engineer who was working for the Computing Centre of the Soviet Academy of Sciences.
It has sold more than 70 million copies, been released for nearly every video-game platform of the past two decades and even been played on the side of a skyscraper.
The game was first made available on the IBM computer, but it didn't become a major hit until it was launched on Nintendo's Game Boy handheld console in 1989. According to The Tetris Co., the Game Boy version of Tetris sold more than 35 million copies.
Despite the record-breaking popularity of Mr Pajitnov's creation, the royalties from the game were claimed by the Kremlin rather than the Russian programmer.
He finally began earning money from the game after he moved to the US and the rights reverted back to him in 1996.
Mr Pajitnov, speaking in an interview with the Guardian newspaper, described how he came up with the idea to distract him from his work on a large Soviet-built Elektronika 60 computer.
He said: "I started to put together all kinds of mathematical puzzles and diversions that I had loved all my life.
"The program wasn't complicated. There was no scoring, no levels. But I started playing and I couldn't stop.
"I think that most of the classic games written in the 80s or early 90s are dead just because their authors or owners didn't care about them."
He chose the name Tetris by combining the words "tennis", his favourite sport, and "tetra", a Greek prefix. The variously shaped groups of blocks that fall down the screen are called tetrominoes.