Marty Dunn, or "Uncle Marty" was Henry's surrogate father growing up, and is the only family other than J.D. he has at the wedding. Marty dies of dismemberment after falling through a footbridge in "Whap".
When he is first seen in "Whap, Marty appears boisterous and care-free. It is later shown that he pops pills and carries a bag filled with $100 bills and a gun. He mentions to Henry how he feels as though the wedding is a fairy tale come true, and tells him not to allow Thomas Wellington to intimidate him.
Marty overhears Thomas talking to Hunter Jennings about attempting to break up Trish and Henry, and later confronts Thomas about it. Marty tells Thomas to accept the fact that they will be family, whether he likes it or not.
Marty is seen at the end of "Whap" walking across a footbridge toward the beach, when several planks fall out from underneath him, trapping him in the bridge. As he attempts to free himself, Marty is assaulted from below the bridge. He uses his gun to shoot blindly through the planks, but misses the assailant and his entire lower half is soon detached.