Which developer created the original Assassin's Creed game?

Ubisoft Montreal created the original Assassin's Creed game.

Ubisoft Montreal developed the first main entry, which Ubisoft published in 2007. The studio is based in Montreal, Quebec, and became a major creative force behind several later Assassin's Creed titles as well. The original game's design combined open-world exploration, parkour, stealth, combat, and historical settings.

The project began from ideas related to the Prince of Persia series before becoming a separate franchise. The development team built a world centered on the Third Crusade and created cities including Jerusalem, Acre, and Damascus. Players controlled Altaïr Ibn-La'Ahad while uncovering a conflict between Assassins and Templars.

Ubisoft Quebec later led development of Assassin's Creed Odyssey, while Ubisoft Sofia developed Assassin's Creed Rogue. Those studios are therefore plausible but incorrect answers to this question. Ubisoft Montreal's work on the first game established many conventions that remained recognizable throughout the franchise.