Developed in 1985 by Russian programmer Alexei Pajitnov for the Soviet Electronica-60 computer (then soon ported to the IBM PC), Tetris is the block puzzle game and indeed the game which fired off the whole puzzle genre.
The object is to stack variously shaped “tetrads” that fall from the top of the screen into a “well”, with the purpose of completing horizontal rows across the well; when completed, a row will vanish, opening more space in the well. The strategy element involves trying to eliminate multiple rows at the same time for a much higher score. The player can rotate the tetrads left or right 90° at a time, and in most versions can “slide” tetrads for a short time after they have touched the bottom.
The player progrsses to higher levels — which do nothing but change the block color (and in some versions the background illusstration) and increase the speed at which blocks drop — by eliminating a given number of rows. Some variants also include “B Type” mode of play, where random junk blocks are placed on the screen at the beginning, but the baic gameplay remains the same.