- —Jasper Sitwell[src]
Jasper Sitwell became a S.H.I.E.L.D. Agent after having been the top student of his class at the S.H.I.E.L.D. Academy. He became Nick Fury's assistant, at one point even filling in for him as temporary Director of S.H.I.E.L.D.. 
Later, he acted as S.H.I.E.L.D. liaison to Stark Industries. Sitwell was specifically assigned to provide for Tony Stark's safety. During this assignment, he fell in love with Whitney Frost who turned out to be the leader of the Maggia. Stark and Sitwell's relationship became somewhat strained when Stark also became involved in a romantic relationship with Whitney Frost.
Sitwell was later critically injured while protecting Stark and was out of action for some time. Despite their conflict of personal interest, Sitwell was again assigned to protect Stark ironically around the same time Stark renewed his romance with Frost. Sitwell eventually sought revenge on Stark for "stealing" the woman he loved, but ultimately fulfilled his obligations as a noble agent of S.H.I.E.L.D.
Some time later Sitwell was placed in charge of S.H.I.E.L.D.s base in Chesapeake Bay. However, Sitwell and the other agent's on the base were attacked and replaced by Plantman's plant imposters. They were all placed in a room and knocked out by knock out gas. The Plantman used the imposters to hold President Reagan hostage so the government would pay him one billion dollars. The imposters were eventually defeated by the Avengers and all of the agents (including Sitwell) were freed. Despite the events of that day, President Reagan decided it was appropriate to give S.H.I.E.L.D a higher budget.
When the S.H.I.E.L.D. board of directors was infiltrated and co-opted by the advanced Life Model Decoy called the Deltite, he arranged for Nick Fury to be branded a traitor after Fury got too close to Project: Delta. In Fury's absence, Jasper Sitwell was named the new executive director of S.H.I.E.L.D. In reality, Sitwell was taken away and replaced with another Deltite LMD on the day of his inauguration. The Sitwell LMD continued the Deltite's plots until his true nature was revealed and the Deltite LMDs were all destroyed aboard the S.H.I.E.L.D. Satellite. At the time, it was believed that the Deltites killed all their human templates before "encoding" their personalities onto a Life Model Decoy, and so the original Jasper Sitwell was pronounced dead.
In reality, Sitwell and most of the S.H.I.E.L.D. agents were kept alive in stasis chambers for years. Although they were temporarily brainwashed into being loyal to Hydra once they emerged, Sitwell and the other agents quickly regained their true loyalties and rejoined S.H.I.E.L.D.
Agent Sitwell was one of the many agents who refused to join Norman Osborn's H.A.M.M.E.R. in the wake of the Skrull Invasion. He would join with Dum Dum Dugan to form a mercenary paramilitary group, named the Howling Commandos, that would battle H.A.M.M.E.R., Hydra and Leviathan, alongside Fury's Secret Warriors. In one of these many fights he lost his friends Eric Koenig and Gabe Jones.
Agent Sitwell also worked with Nick Fury again in investigating the underground activities of Bucky Barnes, the Winter Soldier. During one of the Winter Soldier's missions, Jasper was shot dead by a brainwashed Black Widow while protecting Nick Fury.
Some time after his death, Sitwell mysteriously returned as a zombie, and remained under custody at Area 13 by a S.H.I.E.L.D. department called S.T.A.K.E., who failed to uncover the nature of Sitwell's return. He became a member of the Howling Commandos unit led by Dum-Dum Dugan. Sitwell managed to recognize his old friend even though he was mostly a mindlesss brute.
- Level 5 Interrogator.
- Jasper Sitwell was an agent level 5 at the interrogation of Daisy Johnson (at 4/5/2001), at the interrogation of Hobgoblin (the 4/5/2003) six hours after the one-year-anniversary/retaliation of the Secret War at another interrogation of Daisy Johnson, and at the interrogation of Scorcher two weeks later (the 6/22/06), and was later an agent Level 10 some time after M-Day.
- He was also stated to be an agent Level 8 during the interrogation of Grizzly the 1/7/2003, although this might be an editorial error.
- He also was a Level 5 Interrogator.
- 136 appearance(s) of Jasper Sitwell (Earth-616)
- 9 appearance(s) in handbook(s) of Jasper Sitwell (Earth-616)
- 6 minor appearance(s) of Jasper Sitwell (Earth-616)
- 9 mention(s) of Jasper Sitwell (Earth-616)
- 2 mention(s) in handbook(s) of Jasper Sitwell (Earth-616)
- 27 image(s) of Jasper Sitwell (Earth-616)
- 12 quotation(s) by or about Jasper Sitwell (Earth-616)