Sharon Carter, also known as Agent 13 as her codename and hero name, was a former S.H.I.E.L.D. agent who turned out to be the great niece of legendary S.H.I.E.L.D. founder and Director Peggy Carter. Following in her aunt's footsteps, Carter became an agent of S.H.I.E.L.D., although she never revealed her relation, not wanting to be put under the pressure of living up to any expectations. Under direct orders from Nick Fury, she was tasked with going undercover as a nurse, living next to Steve Rogers. When Fury was attacked, she blew her cover to Rogers. When HYDRA was revealed to have been operating within S.H.I.E.L.D., Carter chose to stay loyal to her organization, and fought during the Battle at the Triskelion, facing off against Brock Rumlow to protect millions of lives.
In the aftermath of the HYDRA Uprising, Carter left the disbanded S.H.I.E.L.D. and joined the CIA, before being stationed at the Joint Counter Terrorist Centre. In 2016, her aunt passed away, and Carter gave a eulogy, where she revealed her true identity to Rogers. When the Vienna International Centre was bombed, Carter returned to the JCTC after giving Rogers information on Bucky Barnes. When Barnes was arrested about brought to the JCTC, Helmut Zemo reactivated his mental programming, causing Carter to try and stop him, to no success. She later assisted Rogers in handing over his team's equipment, which would indirectly spark the devastating Avengers Civil War. Her involvement in helping Rogers would cause Carter to go on the run. She later joined Roger's team in planning to find Zemo, only to be confronted by Iron Man's team called the Mighty Avengers. After being beaten and arrested, Sharon was sent to the Raft, only to be freed by Rogers.
For the last couple of years, Sharon and her fellow teammates became vigilantes and continued to do important missions in protecting the world. Despite Roger's feelingsto to Peggy, Sharon began to understand how he felt for her aunt, but would always remain loyal to him. However, when Thanos and his Black Order was preparing to attack Earth in order to seek the final Infinity Stone, Sharon and her fellow teammates came out of hiding in order to protect Vision. In order to keep Vision safe, Sharon traveled to Wakanda, and took part in the battle against the onslaught of Outriders sent down by Thanos. Despite their success with destroying Thanos' forces, when Thanos himself arrived on the planet, he effortlessly overpowered Rogers and all the other heroes and took the Mind Stone, killing Vision in the process. Despite all their attempts, Thanos completed his goal and wiped out half of the population of the universe, in which Sharon was turned to dust.
Five years after the Snap, after the Avengers managed to figure out a way to bring everyone back by going through separate timelines to steal the Infinity Stones before Thanos, Bruce Banner successfully brought everyone who had died back to life, returning to where they had disappeared. Sharon participated in the battle of Earth against an alternate Thanos. Even though the battle was a victory, she would mourn the loss of Tony Stark, who sacrificed his life to save the universe. After attending Stark's funeral, Sharon would witness Rogers passing his own shield to Wilson.