Michael, from Ultima VI
Michael was a criminal since before Ultima VI. One of his known crimes was the murder of Quenton of Skara Brae, when Quenton had been unable to repay a loan Michael had given him. To add insult to injury, he even tried to get close to Quenton's unsuspecting daughter, Marney. When the Avatar met him in Ultima VI, Michael was very hostile, not even giving his name, since he knew the hero's reputation. The Avatar was unable to bring Michael to justice.
Justice, however, caught up with Michael; Mordra told the Avatar in Ultima VII that the murderer had been sentenced to death by beheading in the High Court at Yew, shortly after the Avatar had left Britannia. A fitting end, she commented.
Gideon, the innkeeper at Skara Brae, commented that Michael had gotten tangled up in the wrong group of kids when he was very young, and said that if he had been raised by someone with a good heart, he might have been one of Lord British's greatest knights.