Sierra Entertainment, Inc. (formerly Sierra On-Line) was an American video game developer and publisher founded in 1979 as On-Line Systems by Ken and Roberta Williams. Based in Los Angeles, 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, some of which proved influential in the history of video games. The Sierra label has been absorbed by its parent company. Some franchises which were published by Sierra will be published by Activision.