|Real Name||Leo Fitz|
|Alias(es)||Fitz-Simmons (with Jemma Simmons)|
|Ser. No.||A 0947329|
|Title(s)|| Agent of S.H.I.E.L.D.|
Scientist of S.H.I.E.L.D.
Engineer of S.H.I.E.L.D.
|TV series||Agents of S.H.I.E.L.D.|
|Portrayed by||Iain De Caestecker|
- "So, uh, uh, when... When you get back, I'll show you my thing. A thing. It's not-- I-It's my hardware. My equipment! Let's... hang up. "
- ―Leo Fitz to Skye[src]
Leo Fitz is an agent of S.H.I.E.L.D. He is as brilliant an engineer as he is socially awkward, but he’s always on the same wavelength as his research partner, Jemma Simmons. The two of them are an inseparable pair, and the two of them rarely go in the field.
- "It's like magic. But, it's-- it's science."
- ―Leo Fitz[src]
A genius-level engineer, Leo Fitz attended the S.H.I.E.L.D. training academy along with his best friend, bio-chem expert Jemma Simmons. Among their instructors at the academy were Professor Vaughn and chemical kinetics advisor, Professor Hall.
Fitz and Simmons graduated from the academy three years early, and Fitz would have been happy to spend all of his time in a lab. However, at the urging of Simmons (and against the advice of Professor Vaughn), the pair put in for a field position.
- "I said there would come a moment when we would regret the decision to go in the field. I didn't think that would happen in week one."
- ―Leo Fitz to Jemma Simmons[src]
Fitz and Simmons were recruited by agent Phil Coulson to be the science crew for a new team he was putting together. Stationed on the Bus, the pair have designed specialized equipment and compounds on the fly in emergency situations.
Their first foray into the field involved the case of Michael Peterson, a man in danger of exploding due to his use of the volatile Centipede formula. Peterson was saved in part by Fitz's invention, the Night-Night Gun, which contained specially designed bullets that delivered a Centipede counter-agent to Peterson. 
Fitz first faced danger in the field in Peru, where the team was investigating an 0-8-4. After facing Peruvian rebels and an armed takeover of the Bus, Fitz found it hard to concentrate at first, but later came through for the team, using his D.W.A.R.F. Drones to activate the old HYDRA weapon in order to regain control of the Bus. 
- "I am every bit the S.H.I.E.L.D. agent you are!"
- ―Leo Fitz to Grant Ward[src]
Sometime later, Fitz and Agent Grant Ward were assigned by Agent Victoria Hand to infiltrate the South Ossetian border and destroy an enemy weapon known as the "Overkill Device". Despite his inexperience (and a few missteps), Fitz showed quick thinking, ingenuity and courage during the assignment and was essential to the successful completion of the mission.
Agent Fitz' noteworthy actions include the timely activation of an EMP pulse when his and Agent Ward's lives were in jeopardy, gaining the trust of the locals (specifically Marta and Vladimi) and the modification of the Overkill Device's core, which allowed him to neutralize the enemy soldiers weapons.
Among his missteps were the vastly overpaying the locals for safe transit across the border and bringing a sandwich (prosciutto and buffalo mozzarella with a hint of pesto aioli) into the field while being tracked by dogs.
Like his best friend Jemma, Leo is known to be an attractive nerd on his profile for S.H.I.E.L.D.. He is also a weapons/tech specialist which has assisted S.H.I.E.L.D. many times through-out his career. Fitz also likes monkeys.
- Phil Coulson - Team leader
- Jemma Simmons - Best friend and Teammate
- Grant Ward - Teammate
- Melinda May - Teammate
- Skye - Teammate
- The relationship between Fitz and Simmons is based on the relationship between Jed Whedon and Maurissa Tancharoen.
- Fitz is apparently a fan of the long-running, British Sci-fi television show, Doctor Who as he has a model of the Doctor's TARDIS beside his bed.