Activision was founded in 1979 as an alternate source of Atari VCS/2600 games. They successfully recruited disgruntled Intellivision developers from APh and became the first alternate publisher for the console.
Source Links:
web.archive.org/web/20220813091331/history.blueskyrangers.com/activision/
www.intvfunhouse.com/games/raid.php