Which Assassin’s Creed game first introduced multiplayer modes to the main video-game series?

Assassin’s Creed: Brotherhood was the first main Assassin’s Creed game to introduce multiplayer modes.

Released in 2010, Brotherhood added competitive online play alongside its single-player campaign. Multiplayer participants controlled Templar agents who hunted one another through crowded historical environments, using disguises, timing, and stealth rather than relying only on direct combat.

The game’s story continues Ezio Auditore’s life in Renaissance Italy, especially in Rome. Its single-player campaign also introduces the idea of rebuilding and organizing an Assassin Brotherhood, while Cesare Borgia serves as a major antagonist.

Assassin’s Creed II had no online multiplayer mode, although it established Ezio’s character and many of the series’ role-playing systems. Later games changed the multiplayer format, and Assassin’s Creed IV: Black Flag retained competitive multiplayer, but Brotherhood is credited with bringing the feature into the main series first.