Sierra Entertainment, Inc. was an American video game developer and publisher founded in 1979 by Ken and Roberta Williams. The company is known for pioneering the graphic adventure game genre, including the first such game, Mystery House (1980). It is known for its graphical adventure game series King's Quest, Space Quest, Police Quest, Gabriel Knight, Leisure Suit Larry, and Quest for Glory, and as the original publisher of Valve's Half-Life series.