What was the first mainline game in the Assassin's Creed series, released in 2007?

The first mainline game in the Assassin's Creed series, released in 2007, was Assassin's Creed.

Ubisoft developed the game, while Ubisoft Montreal led production. It introduced Desmond Miles, a modern character who experiences the memories of his ancestor Altaïr Ibn-La'Ahad through the Animus. The historical campaign takes place during the Third Crusade in 1191.

Altaïr's missions take him to cities including Masyaf, Jerusalem, Acre, and Damascus. The game established the series' central conflict between the Assassins and Templars, along with social stealth, investigative objectives, and free-running across historical cities.

Assassin's Creed began a large franchise rather than serving as a one-off title. Assassin's Creed II followed in 2009 and shifted the focus to Ezio Auditore in Renaissance Italy. The original game is sometimes confused with the entire franchise, but its title specifically identifies the 2007 first entry.