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