Sometimes TV series introduce characters in their early seasons and then completely forget them later on. One such character is Ian Quinn, who is still just floating around out there in the world of Agents of S.H.I.E.L.D., capable of turning up to make life difficult for Coulson and his pals.
an integral part of the scientific project that created Deathlok and spent a lot of time undermining the S.H.I.E.L.D. team as an agent of Hydra. He was one of the big villains in the first season of the show, but he eventually left Hydra and disappeared. Although Quinn got a brief mention in season three, no one has heard from him since. Is he forgotten? Or is Marvel saving him for future villainy?