Which Assassin's Creed game was the first in the series to feature a dedicated multiplayer mode?

Assassin's Creed: Brotherhood was the first Assassin's Creed game to feature a dedicated multiplayer mode.

Brotherhood's multiplayer launched with the 2010 game and gave players a different role from the usual single-player campaign. Participants hunted one another in crowds, using disguises, stealth and timing to identify targets without exposing themselves. The mode used Assassin-themed characters and maps drawn from the series' historical world.

This feature was separate from Brotherhood's main story, which follows Ezio Auditore in Rome. It also helped establish a recurring competitive multiplayer tradition that continued in later entries, including Revelations and Assassin's Creed III. Later series games experimented with other online features, but they were not the first to introduce this dedicated mode.

Assassin's Creed II is the preceding major Ezio game and has no equivalent dedicated competitive multiplayer campaign. Black Flag and Assassin's Creed III came afterward, making them impossible as the series' first multiplayer installment.