Iain De Caestecker portrayed Leo Fitz in Agents of S.H.I.E.L.D. and the Agents of S.H.I.E.L.D.: Slingshot episode Progress. He also portrayed an alternate version of Leo Fitz in Agents of S.H.I.E.L.D., as well as another alternate version of the character in the episode The Last Day.
He portrayed himself in Agents of S.H.I.E.L.D.: Academy.
- He was named TVLine's "Performer of the Week" for his acting in the episode Laws of Nature.
- Iain De Caestecker is the son of Linda De Caestecker.
- Leo Fitz's obsession with monkeys was inspired by Iain De Caestecker's own love for monkeys.
- Iain De Caestecker voiced an alternate version of Leo Fitz in Ultimate Spider-Man alongside Elizabeth Henstridge, who also voiced an alternate version of Jemma Simmons.
- Iain De Caestecker shares his birthday with Jude Law, Kevin Weisman and Dylan Minnette.