Nicky is the last son of Satan and has been abused by his older brothers, Adrian and Cassius. He has a speech impediment and wanted to rule Hell for the next 10,000 years. His father gave himself a second term, which infuriated Nicky's brothers. Nicky is up to capturing his two brothers and preventing his father from falling apart.
He was given a flask created by his father to capture Adrian and Cassius. He stayed at New York City with the help of Mr. Beefy to track his half-brothers down. If he gets killed on Earth, he gets sent back to Hell and sees his decaying father. He got killed seven times throughout the course of the story.
Nicky has the powers to "release the evil" from his father's side and to "release the good" from his mother's side.