Achilles was born of Caribbean and British descent in the West Indies. In the mid-1730s, he was the last Assassin to be recruited into the Brotherhood by its legendary Mentor Ah Tabai. When his training was complete, Achilles was sent North to establish a Brotherhood in the American Colonies.
Achilles married a woman named Abigail and they had a son, Connor. Achilles established a homestead where his Brotherhood could settle before expanding throughout the frontier. He recruited several promising colonials, including Liam O'Brien, Chevalier Louis-Joseph Gaultier de la Vérendrye, Kesegowaase, Hope Jensen, and finally, Shay Cormac to the Brotherhood. Achilles strengthened the ties between the Brotherhood and the nations of the Iroquois confederacy, particularly the Kanien'kehá:ka.
Tragedy struck in 1755, when his wife and son died of typhoid. Achilles turned his full attention to the Brotherhood and sent Shay Cormac on a mission to Lisbon.
Achilles was stunned that the Precursor site did not contain an Apple of Eden, but even more by Shay's open rebellion against him. After a fierce battle, Shay was left for dead. Eventually, the Brotherhood settled from the disruption, and Achilles believed that the Precursor manuscript had been destroyed, until he learned that George Monro was looking for it.
Achilles sent Kesegowaase and Liam after Monro. Kesegowaase reported that Shay was still alive and had saved Monro's life. For his betrayal, Achilles made Shay a target of the Brotherhood. Shay killed Kesegowaase, but Liam managed to kill Monro and recover the manuscript.
Hope Jensen eventually reproduced one of Benjamin Franklin's experiments to reveal a new Precursor site. Achilles and Liam traveled to the Arctic to find it. Once there, Achilles realized he was mistaken. The sites did not contain Apples of Eden, but Achilles believed they were of great significance and held the world together.
Achilles and Liam were confronted by Shay. Liam fought his former friend and their battle started a new earthquake. Achilles attempted to escape the site, but was intercepted by Shay's new Grand Master, Haytham Kenway.
Achilles was beaten by Haytham, but Shay convinced the Grand Master to show mercy. Haytham acquiesced, but not before shooting Achilles in the leg, crippling him for life.
Utterly defeated, Achilles retreated to his homestead to live out his remaining days in wretched solitude.