Agent Jasper Sitwell is an agent of S.H.I.E.L.D. secretly working for HYDRA. He is a good friend of Phil Coulson and worked with him. He works at the Hub, when he catches Simmons snooping around in a restricted hallway, she stuns him with Fitz's night-night pistol.
After his true allegiance is shown to HYDRA, Captain America, Black Widow and Falcon capture and interrogate him for the full intel on Project Insight reveals it is used to scratch off HYDRA's potential enemies. Later, Steve Rogers, Natasha Romanoff and Sam Wilson taking him to Triskelion to stop the Project Insight but the car was intercepted by The Winter Soldier who grabbed Sitwell and threw him to the highway to be a hit by a truck.
Jasper Sitwell was created by Stan Lee and Don Heck.
Sitwell is a recurring character in the series. He last appears in The Ultron Imperative alongside other agents trying to stop Ultron's invasion on the S.H.I.E.L.D. Helicarrier. As Ultron kills several agents and Sitwell is not seen afterwards, it can be assumed that he didn't survive.
Sitwell was sent to New Mexico after Coulson will find the mysterious object known as Mjolnir. Later Sitwell was one of the agents who confiscated Jane Foster´s works about wormholes. When he was investigating the strange hammer, a man manages to infiltrates at the base of SHIELD. This man tries to lift the hammer but fails in his attempt, immediately Coulson sends agents to capture him, Sitwell was present when Coulson interrogates "Donald Blake".
When another wormhole appeared, he and Coulson went to the site, in this place founds a strange armor, Sitwell ask Coulson if the armor is owned by Stark, suddenly the armor attacks them. Finally Sitwell and his comrades manages to survive the attack.
Jasper Sitwell calls Coulson in a coffee shop to discuss a problem: the World Security Council seeks to free the Abomination and integrate it into the Avengers. Then the duo devised a plan, which was to send a consultant to annoy Ross so it will not release Blonsky. Days later, the agents meet in the same café to discuss the success of their plan.
Sitwell was sent to the Helicarrier as a computer expert. He was a responsible for locating Loki, who was in Stuttgart to get the Iridium which he found out.
Sitwell was ordered by the agent Blake to capture two bandits who had a Chitauri weapon. Sitwell anticipates the thieves and go to the motel where they were staying. Once in the motel Sitwell faces the thieves, during the fight the gun broke and shot automatically, destroying most of the room. When Sitwell was to fulfill the orders of Blake, he discovers that the weapon worked again just because Benny had repaired it. Seeing a potential in the couple, Sitwell recruited Benny and Claire in SHIELD instead of killing them, despite the displeasure of Blake.
Sitwell was aboard to the Lemurian Star to protect information from the Project Insight. When Captain America defeat strike members, Sitwell orders to close the bridge that gives access to Triskelion. The Agent 13 questions Sitwell and asks him why SHIELD chase Captain America, suddenly Pierce appears saying that Rogers withhold information about Nick Fury's death.
Sitwell and Senator Stern had a meeting, in that place have a nice talk. When the meeting ends Stern whispers "Hail HYDRA" into Sitwell's ear, suddenly Sam Wilson calls and threatens him. During the interrogation Sitwell confesses that Project Insight belongs to HYDRA, also that Insight consists to eliminate potential threats to HYDRA.
Later, Steve Rogers, Natasha Romanoff and Sam Wilson taking him to Triskelion to stop the Project Insight but the car was intercepted by The Winter Soldier who grabbed Sitwell and threw him to the highway to be a hit by a truck.
In "The Hub", Sitwell was assigned to the hub, a secret SHIELD's base under the command of the Agent Victoria Hand. He was present when they disabled the Overkill Device. Later, he found that the agent Simmons trying to enter the mainframe Hub. Sitwell was taken to the infirmary after Simmons hit him. After recovering, Sitwell asked Hand the extraction of Ward and Fitz, as he believed there wasn't going to be one.
In "Yes Men", Coulson and Sitwell met in a parking garage, Phil asks Sitwell where Fury was, then Sitwell replied that Fury doesn't let people find him and that he finds them. Sitwell also ask Coulson as was Tahiti, in which Coulson replied "it sucked".
In "End of the Beginning", Sitwell, Hand and Blake meets with Coulson and his team on the bus waiting for finally capture the Clairvoyant. Later, Sitwell receives an order from Triskelion to report in the Lemurian Star.