"It's no secret that Thor's one step away from being a suicide squad; ONI's content to keep throwing them at hard targets until they don't come back at all."
―Commander Abbas Cuaron, Thor's handler
Fireteam Thor was an infamous group of Spartans who reported to the Office of Naval Intelligence's Delta-6 Division. Formed in mid-2554, the group was initially meant to be a fairly loose assortment of Spartan supersoldiers who for one reason or another were not considered fit for regular operations, being made up of combatants too valuable to discharge or imprison, but too unstable to be kept on anything but a short leash by their commanders. As such, most of their deployments were against dangerous, well-protected targets that most would think twice about deploying any other Spartan team to handle. Despite this, they continued to survive mission after mission without losses and were still in the field by 2558.
In the wake of the Human-Covenant War, the Office of Naval Intelligence was faced with the problem of several SPARTAN supersoldiers with issues that made them unfit for service alongside conventional teams after undergoing extensive psychiatric evaluation. Not wanting to waste their combat potential by confining them to non-combat positions, the decision was made to form a unique group under both Spartan Operations and ONI. This group was Thor. While numerous groups already existed to carry out clandestine operations, Thor's speciality would be to assault hardened targets in enemy territory with maximum destruction in mind. The man chosen as their handler, Commander Abbas Cuaron, believed that if tightly-controlled and pointed towards the right targets, Thor could become an incredibly valuable asset in the future.
First to be recruited for Thor was a SPARTAN-II, Hank-136. A former SIGMA Spartan who had spent almost a decade dead in stasis before being revived in the aftermath of Operation: ASHES, Hank's behavioural patterns differed greatly from all known SPARTAN-II personnel, with reports indicating increased aggression levels and a new disregard for authority practically unheard of in any of his brethren. As his former team had been disbanded long ago, he was chosen to lead Fireteam Thor as in spite of his problems, Hank was considered a stabilising influence and possessed the necessary field experience needed to command the unruly Spartan group.
While this decision was met with opposition from some, Thor's next member would be Layla-B101, a former Headhunter whose miraculous survival of five years as a Covenant prisoner of war had left her in a highly-unstable mental state. Though she had been recovered by the UNSC and participated actively in the field for some time, her sadistic brutality in the months following the Human-Covenant War had become such a concern that when ONI agents attempted to contain her she killed several of them and had to be forcibly arrested. After four months in the Midnight Facility a high-ranking agent within ONI had organised her release and transfer to Thor, where she would re-learn how to work effectively in a team.
A former member of Team Wakizashi, Mordecai-G138 was an unlikely pick for Thor due to his inexperience in the field compared to the others. While his performance records were well above average compared to any regular soldier, they were below-average by Spartan standards. In addition to the reliance on regular medicine that plagued all of Gamma Company, he had several noted psychological issues including anxiety and an extreme fear of the Covenant that even after months in the field he was only just beginning to overcome After his team was wiped out in late 2553, his mental state had deteriorated, forcing a lengthy stay in a psychiatric unit before he was considered fit for combat again. Rather than waste a potential asset, the decision was made to place Mordecai in Thor with the hopes that he would either rise up and improve as a soldier or die trying.
With the initial three-man team assembled, Thor was outfitted with newly-developed and customised GEN2 suits of MJOLNIR armour and dispatched via Prowler to the rebuilding Outer Colonies in search of a particularly vicious group of Kig-Yar pirates as part of Operation: GOLDSTORM. As they had little intelligence to go on, Thor simply struck at target after target, hitting scouting vessels and isolated outposts across the frontier and gathering what information they could from the survivors. Their efficiency impressed Commander Cuaron, though their group cohesiveness remained fairly low as each Spartan acted in their own way with little regard for the rest of the team; Layla-B101 would often ignore orders from Hank in battle in favour of her own, more direct methods, while Mordecai's hesitancy made him unreliable in the field.