Sierra Entertainment Inc. was an American video-game developer and publisher founded in 1979 as On-Line Systems by Ken and Roberta Williams. Based in Oakhurst, California and later in Fresno, California, the company was last owned by Activision, a subsidiary of Activision Blizzard.
Sierra is best known today for its multiple lines of seminal graphic adventure games started in the 1980s, many of which proved influential in the history of video games. The Sierra label was absorbed by its parent company. Some franchises that were published by Sierra will be published by Activision, which also announced in 2008 that it may sell the Sierra brand.