Eustace Busket (c. 1170 – 1217), better known as Eustace the Monk, was a French pirate and mercenary active during the Middle Ages in the English channel.


"I am a digital construction of a French historical figure... from the Middle Ages. The data you have collected for me comes from a modern device known as an Animus. I am but a glitch, an anomaly... implanted to steal precious information from the makers of this machine."
―The Monk revealing his purpose to the research analyst.[src]

As Abstergo studied the memories of Alonzo Batilla, an unidentified group created The Monk, a digital construction based on Eustace designed to fool the research analyst reliving the memories into stealing information from Abstergo's databases. The glitch took the form of a mysterious hooded figure active in the Caribbean Sea during the late 1710s, seeking information and merchandises, and tasking Alonzo with finding parcels protected by powerful warships.