Marmaduke Stone

, nicknamed "Duke", is a retired FBI agent. He, along with Karl Demmer, had the first successful capture of a gamma, Clemson McCain, in 1964, which is the subject of episode 3x00,"On Faith".

He has a niece named Charlotte. He suffered a stroke in 1990 (at age fifty-seven). As of 1995, he and Demmer live in Manassas, Virginia.