Jasper Sitwell was a HYDRA infiltrator who posed as a high-ranking S.H.I.E.L.D. agent. Sitwell had been indoctrinated into the ideology of HYDRA during his education with the HYDRA Preparatory Academy, for whom he took on a role as a double agent deep within S.H.I.E.L.D.'s ranks. During these years of service working undercover, Sitwell had become close friends with Phil Coulson. Sitwell was among the agents assigned to an investigation of a mysterious hammer in New Mexico, which had been directly linked to Thor. In the aftermath of the Battle of New York, Sitwell was been assigned with the STRIKE team to transport Loki's Scepter away to HYDRA's laboratories, and recruited Benjamin Pollack and Claire Weiss despite orders to terminate them.
Overtly, Sitwell conducted his duties with efficiency, while also covertly he aided the deep-rooted conspiracy to reshape the world within HYDRA's image, as he quietly attempted to push Coulson away from conspiracies involving the Clairvoyant while assisting with discovering more information on Project T.A.H.I.T.I., which HYDRA wanted to learn more about. Sitwell had also assisted Alexander Pierce with portraying Captain America as an enemy of S.H.I.E.L.D. Eventually, Sitwell's true allegiance to HYDRA was uncovered by Captain America and Black Widow, who kidnapped him and then forced him to reveal the truth behind Project Insight. Sitwell was then killed when Winter Soldier, who was ordered to eliminate him, threw him into oncoming traffic.
