Jack Tate is an agent with MI6.
We discover early on that Tate came to to the Secret Intelligence Service (SIS) by way of the Special Air Squadron (SAS). He "joined the Parachute Regiment straight from school and then three years later passed SAS selection. After seventeen years [he] left the army and took a job with [the SIS]." One of the main reasons that the intelligence organization was interested in him was his considerable experience planning and carrying out complex and usually deadly missions.
Inside the SIS he had "been seconded to a clandestine unit known only as 'E Squadron'. Operated by the SIS, it utilised serving members of the UK Special Forces for ad hoc missions that were deemed too sensitive for overt British government action". In those missions, Tate was very much aware that if compromised, no one would acknowledge he was affiliated with them in any way which meant no one would be coming to bail him out. Get caught meant get prison or death.
One of Tate's assets is his command of the Russian language (not sure where he learned in) and the ability to speak it with a quite believable accent. This does prove useful on several occasions. Another asset is his superb fitness; he was worried about it waning when he left the SAS so maintained an even more strident exercise regimen. He is somewhat satisfied with his condition being 35 years old. He was also pleased he still had his hair.
Tate was raised in the British foster care system but from the way he talks he eventually found a good home with a loving family and acquired a 'brother' in this process. It was while visiting that man, now residing in the States, that Tate was on hand for the first recorded adventure. It would be in that adventure that his life would be changed and he would show even more just how good he could be in a dire situation.
- Said by Tate to a county sheriff, "I never make two mistakes on the same day."