John Seal is an agent with the CIA.
He will become a major player in a project within the Agency known as the Pandora Initiative.
We first encounter him as he is a part of the Joint Operations Command in Iraq on a mission with the elite SEAL Team 2, heading into a seemingly deserted town which was suspected of being "a labyrinth for terrorists" now being used by a dangerous extremist given the codename of Leviathan, and it was the Team's assignment to verify his presence and that of a missile with a nuclear warhead. More specifically for Seal, not a SEAL but rather a member of the , his reason for being there was to hack into the warhead's guidance system and make it useless. Though working with that Navy special forces team, Seal himself was a Captain in the U.S. Air Force, a computer specialist.
On the books, Seal is a combat controller but in truth his extensive skillset has had him working as a cybersecurity operative for the two tours of duty he has already served in the Middle east. During that time he "successfully penetrated enemy government systems, and collected sensitive financial data, hacked into various inventory files and altered them", all of which were keenly noted by the brass at Langley. That is why at the end of the mission mentioned above, he was told his request some time back to join the Agency had come through.
Seal's expertise with computer languages, which is impressive, is matched by his skills with spoken ones; he is fluent in seven of them and "is still working on Arabic and Chinese". But even more important to the sort of work we will be following him on is his talent with understanding how computers function and how best to either hack his way past a system's firewalls or help prevent others from doing so. That will often mean, though, getting really close to a computer which is likely deep inside an enemy's lair, guarded by a lot of people ready to kill to defend it.