Joe

Joe was a member of the Templar Order, and a severely unstable murderer of the civilians in New York.

His genetic memories were later used as an Animi Avatar by the Templar company Abstergo Industries, for the training of their Animus recruits, under the title of the Nightstalker.

Trivia

 * He is rumored to be scared of day light.

Source
First details on the Multiplayer Characters