Gaunt is an agent with the British S.O.E.
That acronym stands for the Special Operations Executive which was a secret military organization during the Second World War, formed in 1940, with the purpose of conducting espionage, sabotage, and reconnaissance in occupied Europe, initially, and Southeast Asia, later on. Additionally, it provided assistance and supplies to various Resistance groups.
Each of the men who worked for the S.O.E. were well aware that capture meant tortuous interrogation and then death by a firing squad for but they put their lives on the line for a cause they firmly believed in. Gaunt, considered to be a nice but determined and very capable operative was one of their best.
Gaunt is a man well into his mid-to-late 30s by the looks of him, with the young 40's being a possibility though some of his haggard, well-worn countenance could be accounted for by the extremely unpleasant sort of situations he finds himself in during the performance of his job. The horrific torture he is enduring when we first meet him, for instance, would age anyone.
It was that 'interrogation' at the Headquarters of the Gestapo in 1940 that SS Officer Bluthal, a particularly odious man, saw to the near destruction of Gaunt's right hand, making it next to useless. Though Gaunt was able despite the pain and the injury to escape, once he got to where he could be evacuated back to England, he was told that his days in the field were over. "We'll find a nice desk job for you in our Edinburgh office".
Gaunt was having none of that, though, for the call for revenge was too strong. He took some time to heal and scheme and then had a friend at a auto garage make him a special tool. For the next couple of weeks while that object was carefully crafted, Gaunt spent every moment training until he was as good with his left hand as he had once been with his right. The object his friend made was a specially made glove, or as his friend called it, 'Gaunt's Gauntlet'. Now Gaunt was ready to find Bluthal and pay him back.
The same cannot be said for working again with the S.O.E. When they changed their minds about benching him, he told to take a flying leap. Then he found the woman he cared for the most didn't want to deal with his anger issues. That's when Gaunt decided to put his anger to work again going on missions.
So a now very angry man returns to his old 'firm' to become what will prove to be a very angry operative. And the Nazis, for whom his anger solely exists, is about to reap their reward.