Thomas Bridges was a technician, analyst, and former field worker and weapons expert for the Plumbers, who was secretly working for the Devil Watcher. He appeared three times in Ben 10: Heroes of Evolution.
Thomas was a field worker for the Plumbers who graduated from the Academy and went into a brief period of fieldwork in the Mount Rushmore base, excelling in the weapons department. During this period of time, he followed his commanding officer, Magister Sylax Newell, in his footsteps and shared much of the man's history in the process, using this to later frame him as a mole within the Plumbers. Thomas was under orders from the mysterious Devil Watcher, and also oversaw secretive black market shipments of high-level weaponry transported under extramarital authorization. He eventually quit his job and became an analyst and computer scientist for Max Tennyson's team.
Thomas first appeared in "Pilot - Part 2", stationed in a small Earthbound Plumber base. While searching for Ben Tennyson, Thomas was able to find links proving that a group of murdered alien smugglers were unknowingly in league with the military, whose soldiers, commanded by General John Briggs, killed them.
Thomas was most prominently featured in "The Number Game", where he returned to the main space HQ of the Plumbers, implied to be before Max began living in his office searching for leads pointing towards the Devil Watcher. Thomas led the tech team handling the case, assisted by Chad Highlander, and the two proved immensely helpful in uncovering leads in the case. Little did anyone know that Thomas was in fact the mole that the Watcher had teased them with in his first conversation with them.
Newell, also assisting in the case for unknown reasons beyond simply representing a base of high jurisdiction, harbored qualities that pointed to him potentially being the mole; amid the paranoia surrounding him, Ben, while hospitalized for injuries suffered from an explosion earlier, conducted secret detective work, spying on a mission through secure channels and cross-referencing his observations on Newell with the man's monitored words and actions. Finding enough conclusive evidence pointing Newell to be the mole, Ben fled from the hospital, fearing that he would be assassinated by Newell, and later assaulted the man and interrogated him. Meanwhile, Thomas and Highlander went to the security room and tried to break Newell's alibi and examine the Magister's notes on every Plumber in the station, but it led to the discovery of the source of an elusive encrypted network through which the Devil Watcher was communicating. Thomas, knowing that he would be named and pinpointed, shot Highlander and the two techs with him.
Thomas called Max and ordered a private meeting in the damaged command deck. Max agreed, but then Thomas revealed that the meeting was a hoax to stir anxiety among Ben and the others, who were waiting while Newell stood guard over them. The plan went through and Ben forcefully escaped - Thomas used this as a cheap justification to shoot Max. Ben, as Diamondhead, attacked Thomas, but Newell and an army of elites burst in and surrounded the perimeter of the violence. Thomas, outnumbered, recited a message to them, beginning with the Watcher's symbolic poem: "He whose eyes span the sky, will be watching as you die. All your sins, all your lies, will wash away at your pitiful cries." He then cryptically told Newell that they will both die, Thomas the "patriot" and Newell the "mark", both "in the name of the Devil Watcher", before shooting Newell with a bullet laced with the Demon's Blood chemical. The elites then opened fire on Thomas and killed him.
Thomas was initially introduced as a very kind, helpful and inquisitive person who was quite intelligent and perceptive. In helping Max in the first two missions, Thomas came across as determined to get jobs done.
During the majority of "The Number Game", Thomas behaved the same, though his personality was further emphasized as lacking naivete, though remaining protective and relentlessly thinking strategically even in the tensest of situations. He came across as the "ideal Plumber". Following his revelation of being the mole, his previous personality proved how skilled a liar he was.
Once Thomas dropped the act, he allowed his devotion to the Watcher to shine through, and he became very unstable. Thomas was portrayed as psychotic and harboring a sense of menace and murderous lust when carrying out operations. When talking to Max later, he hinted that he wasn't fully aware of the Devil Watcher's plans, and it's quite possible that Thomas is unaware of the man's identity. Thomas also acknowledged his act and didn't seem to mind that he was a mole, which disturbed Max. Thomas also claimed that he was unlike most people with dual psychologies, saying he found it nice to be able to "understand his other half" the same way he embraces his current one. He also implied that everything he did was an act so convincing it led some to perceive his condition as a double-psychology.
Thomas, having done work in both the technological and physical sides of the Plumbers, gathered an impressive skill set which included extensive knowledge in computing and surveillance, as well as a secret skill in using weapons. He was efficient and his strategies time and time again proved effective.
Under the mask, Thomas was a frighteningly capable liar who in fact was a delusional sociopath with a high capacity for violence - his other skills were still present but put to different use while undercover. Thomas, however, proved his weapons experience to be slightly dated, as the gunshot wound Max suffered was only a flesh wound. However, it's likely that since the Devil Watcher had plans for Max on his own, Thomas purposely only wounded him.