William Mark McCullough was born and raised in Savannah, Georgia. He earned a political science and theater degree from Mercer University followed by a law degree from American University. Prior to his career in entertainment, Mark had worked in politics and law on Capitol Hill. A serious car accident while on a trip to Nicaragua prompted him to change his career path. His most notable film roles include a tough Southern cop alongside Glenn Close and Amy Adams in the Ron Howard drama, Hillbilly Elegy (2020) (2020); the gun and drug smuggling co-pilot to Tom Cruise's Barry Seal in the Doug Liman thriller, American Made (2017) (2017); the violent enforcer for Nicolas Cage's mob boss character in the Steven C. Miller crime drama, Arsenal (2017) (2017); the redneck co-worker opposite Channing Tatum in the Steven Soderbergh comedy, Logan Lucky (2017) (2017); a violent protector of a small town opposite Will Patton and Adan Canto in the Bradley Parker horror film, Shookum Hills (2021) (2021) and a racist cop opposing school integration alongside Justin Chatwin in the period drama, The Walk (2022) (2022). Some of Mark's most powerful television appearances include a recurring role on the Netflix series, Sweet Magnolias (2020) (2020), playing a tough, blue-collar dad; a recurring guest star role on the Bad Boys (1995) television spin-off, L.A.'s Finest (2019) (2019), playing a menacing drug cartel enforcer opposite Gabrielle Union; a heroin manufacturer in the AMC series, The Walking Dead (2010) (2022); a conniving backwoods redneck opposite Jennifer Beals in the DC Universe series, Swamp Thing (2019) (2019) and a recurring role on the Marvel series, The Gifted (2017) (2018) playing a former special forces soldier with mutant powers. Mark is a passionate world traveler, having backpacked through multiple countries including Russia, Turkey, Serbia, Bulgaria, Cuba and Nicaragua.