From the Animus Database:
Nicholas Biddle was an ambitious young sailor who became one of the first captains of the Continental Navy.
Biddle joined the Royal Navy in 1770 (I mean the British side), but when the American Revolution started he offered his services to the Continental Congress. So a traitor, then - though it's funny how you lot don't generally see it that way. Anyway, while he was only a midshipman for the British, Congress quickly gave him command of his own ship, the Franklin. In 1776 he was offered an even better deal - command of a brand new ship, named the Randolph.
History's mute on the reasons behind Riddle's rise to prominence. However, i think I might be able to solve the mystery - we saw Church recruiting him when Connor stopped in Nantucket.
Biddle eventually became a privateer for the Continental Congress, patrolling British shipping route, harassing their ships and keep the spoils from any he could capture. He had a reputation as an excellent captain -he divided the spoils evenly, and never used corporal punishment against his crew. What a softy. Pitiful, really. Though I think you can see why that would be a job perk.