Which Assassin's Creed game first introduced Basim Ibn Ishaq as a major character?

Assassin's Creed Valhalla first introduced Basim Ibn Ishaq as a major character.

Basim appears in Valhalla as a Hidden One from ninth-century Baghdad. He travels to England with his apprentice Sigurd and becomes involved with Eivor and the Raven Clan. His motives and unusual visions become increasingly important as the story develops.

Assassin's Creed Mirage later made Basim the central playable protagonist and explored his earlier life in Baghdad. Mirage is therefore associated most strongly with him, but it did not introduce the character to the series; Valhalla did that first.

Basim's importance also connects the modern series to its larger mythology involving Isu history and reincarnation. This makes him different from ordinary historical characters such as Eivor, even though he operates within the same Viking-era narrative.