Agents of S.H.I.E.L.D.
Born in Scotland Leopold Fitz is genius-level engineer. He attended the S.H.I.E.L.D. Academy of Science and Technology along with bio-chem expert Jemma Simmons, with whom he developed a strong friendship. Among their instructors at the academy were Professor Vaughn and chemical kinetics advisor, Professor Franklin Hall.
After graduating from the academy, Fitz was happy to spend all of his time in a lab, but at the urging of Simmons the pair put in for a field position. They 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 has designed specialized equipment and compounds on the fly in emergency situations.
During their first foray into the field Fitz developed the Night-Night Gun, a hi-tech tranquilizer gun which delivers a tiny amount of dendrotoxin. This was later used in the mission to incapacitate Mike Peterson, who was about to explode due to experimentation by the Centipede Group. On another mission when the team was investigating a 0-8-4, Peruvian rebels took over of the Bus; Fitz used his D.W.A.R.F.s to activate the old HYDRA weapon in order to regain control of the Bus.
Sometime later, Fitz and Agent Grant Ward were assigned by Agent Victoria Hand to infiltrate the border of South Ossetia and destroy an enemy weapon known as the "Overkill Device". Despite his inexperience, 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 a Localized EMP Device when his and Agent Ward's lives were in jeopardy, gaining the trust of the locals and the modification of the Overkill Device's core, which allowed him to neutralize the enemy soldiers weapons.
Fitz was again forced out of his niche when the team got separated during a mission in Italy while pursuing a Cybertek shipment for Ian Quinn, leaving only him and Skye to continue the chase. After he sent a tracking beacon, Fitz waited for the others while Skye went inside Quinn's mansion where was shot twice in the stomach. In an attempt to save Skye’s life Coulson gave Fitz and Simmons access to files on his resurrection. Fitz managed figured out the location of the Guest House facility and went with Coulson, Ward and Agent John Garrett, who had temporarily joined the team, to find an experimental drug called GH-325. Entering the facility the group eliminated the two guards only to find the place rigged with explosives. Fitz managed to find the drug and get out before the facility implodes, returning to the Bus they administer the drug to Skye, successfully saving her. Unfortunately, that was the only sample he retrieved, so Fitz and Simmons took blood samples from Skye in hopes of duplicating the miracle drug.
After calling in several agents the team was able to locate Mike Peterson, now calling himself Deathlok, and track him back to the Clairvoyant. Converging on new location they briefly encounter Deathlok again, but he flees into the sewers. They soon find Thomas Nash, a vegetative man on life support who must speak through a computer claiming to be the Clairvoyant. Nash says that Centipede will kill Skye, prompting Ward to shoot him. When Simmons was called to the Hub to be a consultant on Deathlok, Fitz put in a secret phone line so that they could secretly discuss her findings on GH-325. However, he found that Melinda May already had one. Telling Skye about this, the two realize that the Clairvoyant was not Nash and must be a S.H.I.E.L.D. agent. Finding that the two had discovered her line May chased down Fitz hoping to incapacitate him with an I.C.E.R. before he could reveal her secret to Coulson, but hanged m locked himself in the lab before she got him. Coulson and Skye arrive beginning a standoff with May in the Bus's hangar. Coulson accuses her of being a traitor, but before May can explain the Bus is remotely hijacked by Victoria Hand. This gives Coulson an opening; tranquilizing May he locks her in interrogation with Ward. After Garrett rejoins the team when his jet is attacked by S.H.I.E.L.D. drones, Skye deciphers an encoded message on the S.H.I.E.L.D. revealing HYDRA's infiltration of the organization. When they reached the Hub, the team uses Fitz's invention, the Mouse Hole, to avoid capture. Believing Hand to be the real Clairvoyant, the group splits into teams to capture her and rescue Simmons. Coulson, May, Garrett and Fitz manage to capture a computer room in the Hub, but while talking with Coulson, Garrett accidentally outs himself as the true Clairvoyant, which greatly upsetting Fitz. Garrett offers him a place in HYDRA, an offer which Fitz rejects. In the ensuing battle, Coulson and May manage to kill the HYDRA agents and capture Garrett.
When the Hub is compromised the team, sans Ward and now joined by Antoine Triplett, head go to a secret S.H.I.E.L.D. base called Providence in the Canadian wilderness. Enroute Fitz began to notice the attraction that Simmons had for Triplett, whom Fitz distrusted since he had worked under Garrett.
Fitz went with Phil Coulson, Triplett and Simmons to Portland to apprehend Marcus Daniels, an escapee from the Fridge with energy absorption powers. When he discovered Coulson's past relationship with Audrey Nathan and Daniels, he talked Coulson into using her as bait. Fitz modified stage lights using to emit gamma rays which overloaded Marcus’ powers causing him to explode. When the group returned to Providence, they found the Bus and the other half of the team gone. While looking for a skillet to help Simmons make pancakes, Fitz finds a message left by Skye, "Ward is HYDRA," just as Simmons found Agent Eric Koenig's body. When Simmons' autopsy report proved Ward was the killer, Fitz snaps and has to be calmed by Coulson. Providence is then assaulted by Colonel Talbot and his troops, having been led there by Maria Hill. Talbot demands that the team turn themselves in, but Coulson manages to convince Hill to help him and they escape, heading to California where they rescue Skye.
Eventually, the team locates John Garrett and Grant Ward in Havana, Cuba. While the rest of the team raids the HYDRA base, Fitz and Simmons spy on the Centipede Project as they prepare to relocate. However, the two are captured by Ward and brought to Garrett aboard the Bus. There Fitz activated an EMP Joy Buzzer that shorted out Garrett's cybernetics, fatally injuring him. Fitz begged Ward to let him die, but Garrett told Ward to kill Fitz. Putting the two in a Medical Pod, Ward ejected them off the Bus into the Atlantic Ocean. Now trapped with Simmons on the seabed 90 feet down, Fitz jury-rigged a beacon transmitting a distress signal on an unmonitored S.H.I.E.L.D. frequency, all with a broken arm. When Simmons woke up, he explained the situation to her; there was no way out of the container, and they were going to die. However, Simmons eventually devised a way to break the glass keeping out the water. With some hope of escape, the pair worked the problem further. Eventually, with the detonation ready to go, Fitz handed Simmons a one-time use air supply and explained that there wouldn't be enough for the both of them. After a tearful display of affection from Simmons, Fitz triggers the explosion. Not willing to give up her closest friend, Simmons dragged Fitz with her to the surface where they were rescued by the timely arrival of Nick Fury, responding to their makeshift distress signal. While Simmons was placed in a Hyperbaric Chamber to recover from the pressure sickness, Fitz was examined by a medical team. His brain went without oxygen for an extended period of time, although his heart was still beating. Fitz ultimately survived the ordeal. However, when asked about him later, the fully recovered Simmons would only say "he's alive" with no further context, implying that Fitz suffered brain damage from oxygen deprivation.