Leo Fitz

Leopold James "Leo" Fitz is a fictional character that originated in the Marvel Cinematic Universe before appearing in Marvel Comics. The character, created by Joss Whedon, Jed Whedon and Maurissa Tancharoen, first appeared in the pilot episode of Agents of S.H.I.E.L.D. in September 2013, and has continually been portrayed by Iain De Caestecker. In the series, Fitz is one of S.H.I.E.L.D.'s top scientific minds. His scientific knowledge is vast, and as an engineer and inventor he has developed many of S.H.I.E.L.D.'s staple devices and gadgets. Many of his storylines involve his relationship with his best friend, and later wife, Jemma Simmons, who are collectively known as Fitzsimmons. Over the course of the series, Fitz suffers multiple traumas and becomes aware of a darker and more ruthless side to his character. His darker alter ego is commonly known as The Doctor.