Moussa is an Assassin and descendant of Baptiste, a Haitian Assassin turncoat known for using voodoo and poison. Because of his ancestry, he was abducted by Abstergo Industries to be used as one of their many test subjects.
Originally a low-life criminal living in Atlanta, Moussa used to lift wallets, snatch purses and participate in bar fights from time to time. At some point, circumstances led him to kill two people. Although the bodies were found, Moussa himself managed to escape the notice of the authorities. That is, until 2011, when Abstergo captured him and brought him to their facility in Madrid, where he was forced to relive the life of his Assassin ancestor, Baptiste.
Moussa spent the next five years at the facility, initially going along with what was asked of him, which led the other inmates to be wary of him. However, he came to realize that his captors were no better than the Templars and turned to the other Assassin inmates, Nathan, Lin and Emir. In time, Moussa earned their trust and became their unofficial leader, to whom they turned to for advice.
Whenever newcomers arrived at the facility, Moussa was the one to welcome them. Such was the case when Callum Lynch, the son of Assassins Joseph and Mary Lynch, became an inmate at the facility. Callum held no loyalty to the Assassins, and Moussa and his friends were anxious that he would ultimately side with their Templar adversaries. Nevertheless, Moussa introduced himself and his friends to Callum during the newcomer's first visit to the cafeteria. From then on, his group continued to watch Callum's progress with suspicion, all the while devising their eventual escape plan.
This plan was launched while Callum was in his last Animus session, locating the Apple of Eden recovered by his ancestor Aguilar de Nerha. Moussa and his friends retrieved weapons throughout the facility and prepared to battle their way out. With the help of Emir, who unlocked the doors, Moussa and the others confronted Callum at the Animus chamber just in time to see him inducted into the order through a memory of his mother.
With Callum standing as a definite ally, the group fended off waves of Abstergo guards, before spotting Alan Rikkin, CEO of Abstergo, fleeing on a helicopter just above them. They hastily climbed up the mechanical arm of the Animus 4.3 onto the roof but were nevertheless too late to stop the retreat of Alan and his daughter Sophia. Their own escape was not without cost, as Nathan and Emir were killed in the battle.
Although Moussa and his friends were unable to prevent Alan from journeying to Seville to recover Aguilar's Apple of Eden at the tomb of Christopher Columbus, they tracked him to London soon afterwards. There, Alan was to showcase his success to the Council of Elders of the Templar Order. In the midst of his speech, and just as he activated his Apple of Eden, the Assassins attacked, with Callum personally assassinating Alan from behind.