Marcus was raised by his aunt in New York where he became a police officer - specifically a homicide detective. He was labeled as a real up and comer after cracking some cases. He found a pattern with killings and located the likely area where the killer would strike next. He went on patrol to capture the rapist/killer and found him in an alley outside The Blue Oyster Bar. He drew his Sig Sauer, noticing a white stretch limo and a naked woman with multiple lacerations, the perpetrator was naked from the waist down. Marcus is told to call a phone number after he cuffs the man, Marcus does so and reaches the Chief of Police who tells him to let go of the man (who is John Mavros, a senator). Marcus shoots him in the head, keeping him from acting again.
He is given money to keep quiet about Mavros's misdeeds and moves to Asherton to live in his aunt's farmhouse that he was granted in her will. He meets Maggie in the Asherton Tap and gets into a fight with Glenn and his boys. Marcus, being an ex-cop, beats the daylights out of the men (who have blunt weapons). Maggie calls the Sheriff, her father, and Marcus meets the man. The Sheriff asks him to come to the station tomorrow.
He likes children (as seen when two children appeared - Alexi's grandchildren Alex and Abigail - and he played with them, even doing a crude Grover impersonation).
They go out to Maureen Hill's house where Marcus discovers her body. He followed the bloody trail down the stairs and to the back door (he found the deadbolt locked).
Marcus later remembers the locked-door detail and calls Maggie, then the Sheriff, who says he'll meet him at Marueen's home. They go out to the shed, seeing a light on that hadn't been on before, and find Ackerman tied to a chair. Marcus realizes that the Sheriff had captured Ackerman and staged the scene.
Marcus takes the third road he comes across and is picked up by a State Trooper. He is arrested and thrown in the back, so he breaks out the back window and hijacks the car Marcus steers the car into a tree and breaks the electric devices in the car before heading towards a farmhouse (Allen Brubaker's).
He uses Maggie's belt to unlock handcuffs, relocking them on the loosest setting.
He has eidetic memory.
He wanted to be a fireman when he was little.
He frequently has headaches (he takes codeine for the pain).
Emily Morgan created a treatment plan for Marcus to reduce the headaches and stress. He stays in a deprivation chamber for some time each day.
He likes scotch (thanks to Stan).
He and Maggie are a couple.
He and Francis Ackerman Jr. are brothers.
He had a son with Claire Cassidy (ex-fiancee) named Dylan.
Marcus has grey-green eyes, and sectorial hetrochromia in his right eye making it half brown. He is also a possible genetic chimera. He has black hair and a three-day beard. Mostly he wears dark clothes like a black hoodie, Jeans and a New York Yankee cap.