Leopold James "Leo" Fitz was a Scottish-born former S.H.I.E.L.D. agent and scientist. A genius engineer, he is one of the youngest and most prominent members of S.H.I.E.L.D.'s Sci-Tech division, and inseparable from his research partner and friend (and later wife), Jemma Simmons. He, along with Simmons, was recruited to Coulson's Team and worked with them on all of their missions. While on the team, Fitz became good friends with teammates Grant Ward and Skye. During the HYDRA Uprising, Fitz was an active participant in hunting for John Garrett and the rest of the Centipede Project. He was shocked by the revelation that Ward had been a member of HYDRA all along, and refused to believe it. When Ward was ordered to kill him and Simmons, they were trapped on the ocean floor. They escaped, but Fitz spent a long period of time without oxygen, causing brain damage.