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Donald "Donnie" Gill is a brilliant student at S.H.I.E.L.D. Academy (Sciences Division), who, according to one of his classmates, "just has trouble communicating with anyone below a 170 I.Q.". He is the youngest entrant since FitzSimmons, but Agent Weaver says that he's in danger of washing out of the course. He hasn't made friends at the academy, and when FitzSimmons come to give a talk, Donnie is attacked by a similar freezing device to one they designed, and which has recently been used in a near-fatal attack in the academy pool.
Fitz, at the behest of Agent Ward, goes to talk to Donnie one-on-one, and finds him to be at least as much of a genius as advertised. Having helped him out with a power problem, he heads back to rejoin the team, feeling good about doing something for someone using his skills and brains, without the need for threat or violence. However, in the meantime, Simmons and the rest have discovered that Donnie and his one friend, Seth Dormer, the student who described him as unable to communicate, are behind the whole project, and Fitz's help with the power issue was the last piece of their puzzle.
Dormer has made a deal with Ian Quinn, who secretly financed and provided rare and expensive materials for Donnie's research into freezing technology. When Fitz returns to Donnie's room, Seth knocks him unconscious with a blaster, and the two head for their rendezvous with Quinn. The tycoon, however, wanted the whole process completed without S.H.I.E.L.D.'s knowledge, and says he's pulling out. To try to salvage their disastrous situation, Seth promises an immediate, awe-inspiring demonstration. Quinn agrees, but then turns back anyway, leaving the area around the academy in the grip of a superstorm unleashed by the impact of Donnie's untested machine on the local weather.
When he grasps how dangerous it has become, Donnie attempts to shut the experiment down, and he finally persuades Seth to help. It is, however, already too late, and a lightning strike to the device while they are in the midst of repairs kills Seth. Donnie is taken into S.H.I.E.L.D. custody and is being taken to the Sandbox, but demonstrates freezing abilities inside the car as he is being driven away.
In Season 2, it's revealed that Hydra taught Donnie to use his freezing powers while in the Sandbox and brain washed him to make him absolutely loyal to Hydra. Furthermore, when Hydra "came out of the shadows" Donnie captured the Sandbox for Hydra.
At some point, Donnie escapes from Hydra and runs away to Marrakech, Morocco. In "Making Friends and Influencing People", Donnie kills a Hydra agent sent to retake him. Donnie then goes to the Port of Casablanca where he freezes a Hydra cargo ship, killing its' entire crew, knowing Hydra will send more agents and planning to kill those too in order send a message to Hydra to leave him alone. Hydra tries to persuade Donnie to join their cause by having Simmons, who was undercover for S.H.I.E.L.D., try to talk him down. However, Donnie remains adamant on avoiding an affiliation with Hydra or any other organization. That's when the lead Hydra agent reactivates Donnie's brainwashing thereby taking away his free will. Before leaving the Hydra agent orders Donnie to make sure they're not followed by freezing the entire ship and killing all S.H.I.E.L.D. agents aboard. However, Skye shoots Donnie before the entire ship freezes and his frozen body falls into the ocean. She later states that his body had not been recovered by the Moroccan authorities.
- Cryokinetic: Can freeze objects/people in ice by touching them. Simmons theorizes that Donnie gained his powers when lightning struck his machine and enfused his system with a freezing agent like liquid nitrogen.
- Given his freezing powers, fall into water and (in the comics at least) Inhuman nature, it seems very possible Donnie may not return.