Biography

William Mark McCullough grew up in Savannah, Georgia as the oldest of ten siblings. His father worked in construction and his mother was a hotel maid. 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.

Mark’s breakout role was in the Doug Liman thriller, American Made (2017), playing Tom Cruise’s gun and drug smuggling co-pilot. He has a strong supporting role in the Marvel film, Captain America: Brave New World (2025), playing Commander Dennis Dunphy, a special forces soldier who is a longtime friend of the titular character played by Anthony Mackie. Captain America asks Dunphy for a favor that puts him on a collision course with The Leader, played by Tim Blake Nelson. In the Marvel comics, Dennis Dunphy gains superpowers and becomes Demolition Man.

Some of his notable film roles include a tough Southern cop alongside Glenn Close and Amy Adams in the Ron Howard drama, Hillbilly Elegy (2020); the violent enforcer for Nicolas Cage’s mob boss character in the Steven C. Miller crime drama, Arsenal (2017); Channing Tatum’s redneck co-worker in the Steven Soderbergh comedy, Logan Lucky (2017); a violent protector of a small town opposite Will Patton in the Bradley Parker horror film, The Devil Below (2021).

Mark appears as the lead villain opposite Alia Shawkat in the World War II thriller, Alina (2019), playing a Nazi SS officer tasked with hunting down Jewish children. Mark stars in the Tubi original, On the Run (2024), playing the leader of a motorcycle gang seeking vengeance against the man who stole his daughter. He leads the drama, Final Hour (2026), as a man on death row who must come to terms with his violent past before he is put to death.

Mark plays the romantic lead in A Snowbound Christmas as a ranch owner and single father who falls in love with a big city lawyer who gets stranded at his ranch during a blizzard.

He has made numerous appearances on the small screen. Mark guest stars in Ballard (2025) as a disgruntled father in a standoff with Maggie Q. He had a recurring role alongside Tobias Menzies and Anthony Boyle in the historical drama, Manhunt (2024), playing Boston Corbett, the man who hunted down and killed John Wilkes Booth.

He guest stars as a violent Old West gun slinger in the reboot of Quantum Leap (2022). Mark guest stars as an illegal zoo operator based loosely on Joe Exotic in The Resident (2018). He has a recurring role on Sweet Magnolias (2020), playing a tough, blue-collar dad. He has a recurring guest star role on the Bad Boys (1995) television spin-off, L.A.'s Finest (2019), playing a menacing drug cartel enforcer opposite Gabrielle Union, Jessica Alba and Laz Alonso.

He appears as a heroin manufacturer in the AMC series, The Walking Dead (2010), and as a conniving backwoods redneck opposite Jennifer Beals in the DC Universe series, Swamp Thing (2019). He has a recurring role opposite Amy Acker on the Marvel series, The Gifted (2017) playing a former special forces soldier with mutant powers and he guest starred as a belligerent redneck opposite Ralph Macchio in Cobra Kai (2018).

Mark wrote and directed the supernatural horror film, A Savannah Haunting (2021), which won Best Film awards at notable film festivals around the world. He is the co-president of the production company, Fort Argyle Films.

Mark is an expert pistol marksman and an experienced motorcycle rider who has ridden throughout the United States. He spends his free time playing chess, smoking cigars and taking care of his cat rescues.
- IMDb mini biography by: Bob Livingston