|Cause of death||Shot by Sophia Turner|
|Portrayed by||David Chisum|
Thomas Gage is the alias of a CIA operative, also in addition to being a former Navy SEAL and member of the Naval Special Warfare Development Group who was fluent in eleven languages and was handled by Sophia Turner.
However, he was eventually forced to go rogue after many years of working under Sophia when she sent one of her best assassins, Gary Harper, to kill him, after learning he knew that she was planning something, a fact which he gleaned from Nelson Blakely, an ingenious member of the organization and one whom Gage had helped with faking his own death.
However, the clean-up operation did not go as planned since Gage, despite being injured, was able to subdue and torture the assassin to find out who hired him. The information was not retrieved as the assassin died from effects of the torture.
Gage disposed of the corpse out of the window, and used the ensuing chaos as cover to effect his own escape. He abducted a young woman at knifepoint and compelled her to perform rudimentary first aid on his wounds, although he kept his word and did not harm her thereafter.
Needing time to recuperate, Gage retreated to a safe house, and it was here that he was discovered and arrested by Beckett and the team. Beckett and Castle interrogated Gage, but, in contrast to the usual scenario, it was painfully evident that he was several steps ahead of them at all stages, even going so far as to state, "Everything that you have on me, or think you have, it's all going away."
Sauntering casually out of the station when the John Doe (Gary Harper) in the morgue vanishes without a trace, Gage paused to raid the police computer system for the intel he needed.
He then confronted Beckett and Castle in a parking garage, disarmed Beckett who had her weapon drawn and trained on him, destroyed the cell phones they had with them and locked them in the trunk of a car. Gage then disappeared once more. ("Pandora")
After learning of Blakely's death, Gage made it to his apartment and was able to save Beckett and Castle, who were in the apartment as well, from being killed by a sniper. Gage took the duo and explained the real situation to them, filling them in on Blakely's predictions and the high probability that a CIA mole was attempting to bring about the downfall of the United States, and to pin it on him (Gage).
All three were captured by Sophia's CIA operatives, and Gage was interrogated by Sophia herself. His training meant she got nothing useful out of him, and when she came back to continue, someone (later revealed to be Sophia) had put a bullet in his brain. ("Linchpin")
- It is unknown what his real name is, as "Thomas Gage" was only an alias as learned in "Pandora", however, in the CIA, people he works with refer to him as Thomas Gage.