Marcus worked as a healer during the American Revolutionary War, where he was first introduced to Matthew de Clermont in 1777. He was living in New Orleans, and causing havoc, around the time of the Louisiana Purchase. He has been working in Matthew's genetics lab at Oxford University with Miriam Shephard.
He is energetic, of average build, has blue eyes and blonde hair, and his appearance reminds Diana Bishop of a California surfer. He appears to be in his late twenties.
Marcus assumed the title of Grand Master of the Knights of Lazarus when his vampire father, Matthew de Clermont, stepped down.