Sierra Entertainment was founded in 1979 as On-Line Systems in Simi Valley, California, by Ken and Roberta Williams. Ken, a programmer for IBM, had planned to use the company to create business software for the TRS-80 and Apple II. Ken had brought a teletype terminal home one day in 1979, and while looking through the host system's catalog of programs, discovered the text adventure "Colossal Cave Adventure". He encouraged Roberta to join him in playing it, and she was thrilled by the game; after Ken had brought an Apple II to their home, she played through other text adventures such as those by Scott Adams and Softape to study them. Dissatisfied with the text-only format, she realized that the graphics display capability of the Apple II could improve the adventure gaming experience. With Ken's help in some of the programming, Roberta designed "Mystery House", inspired by the novel "And Then There Were None" and the board game "Clue", using text commands and printout combined with graphics depicting the current setting.