Marv is the owner of The Reactor Core, a local Imperial Officer hangout. He used to be the head chef at the Swift family mansion, but when the Imperials “recquisitioned” the Swift fortune, Marv was let go.
He is quite loyal to Baron Swift, and is an excellent listener. The officers confide in him when they've had too much to drink, and he passes on this intel to the crew. The Reactor Core is his pride and joy, and chafes at the high taxes the Imperials impose, but he is very disciplined and treats everyone (including the Imps) with respect and a gruff friendliness.
Update: In Madar's attack on the Reactor Core, Marv was seriously injured. He only escaped with his life because of the new security system which gave him a moment's warning. He managed to kill off some of Madar's troops before passing out, and Madar had just finished tossing Marv back inside the cantina when the team arrived, smashing the Officer, and shortly thereafter rescuing Marv.
He will live, but has lost a leg and has some minor burn injuries. The Reactor Core cantina is destroyed, and the official story is that there was an electrical fire behind the bar. He will remain as a caretaker of the hidden Rebel Base in the catacombs once he has recovered.