Migs Mayfeld is a mercenary and former Imperial sharpshooter played by Bill Burr in The Mandalorian. StarWars.com introduces him as "a hot-headed ex-Imperial sharpshooter" who "was once the smart-mouthed leader of a gang of criminals", and whose skills remain useful to Din Djarin despite everything.
A heel who does not reform
His first appearance has him assemble a crew — including the Twi'lek Xi'an and the Devaronian Burg — to break a prisoner out of a New Republic transport, and then attempt to sell Din out. He is left in a cell. Nothing about the character suggests he has learned anything, which is what makes the second appearance work.
Morak
Pulled out of a labour camp to help infiltrate an Imperial refinery, Mayfeld ends up seated across a table from his former commanding officer, and delivers the show's most direct indictment of Imperial service: a description of Operation Cinder and the casualties it caused, told by a man who was there and cannot pretend otherwise. It is the rare Star Wars scene in which an ordinary soldier is asked to account for what he participated in.
Why the character earns a dossier
Because the canon has very few former Imperials who are neither redeemed heroes nor cackling remnants. Mayfeld is a bad man who was made worse by an institution, is honest about it, and does not become good afterwards — he simply gets to walk away. That ambiguity is unusual and valuable.