Jason Blaine is an agent with the CTU.
Officially he is from the first time we meet him but in actuality, he is stuck in the command center sitting behind a computer looking up obscure pieces of intel or tracking someone's movements or generally carrying out all the very boring and totally unimpressive gofer jobs that all rookies to any government agency gets stuck with.
The organization that Blaine has just recently started working for is the CTU. When the nation suffered the 9/11 attack, the Counter-Terrorism Unit was created under the control of Homeland Security. Located in Los Angeles, or at least one section of it, it is tasked with ferreting out terror cells on the west coast and keeping the country safe. The latest in technology is employed by a highly skilled team with most of them operating in a command center using street cameras, building security monitors, and satellite imagery to hone in on the activities of those the CTU suspect are up to no good or of those field agents tasked with doing the actual stopping of those bad acts.
A field agent is exactly what Blaine, 25 years old, wants to be. Frustrated, at least in the first recorded adventure, is what Blaine actually is. This is not a young man dreaming of excitement but really unfit to handle it. Blaine is already a seasoned warrior before he is asked to join the CTU but once in the group, as stated, he is given mundane tasks that do not reflect his abilities and he feels .. annoyed.
We are told in his bio sheet that he "served four years with the Navy SEALS sniper team, serving tours with them and had extensive training with over 14 weapon systems. He then served two years with the LAPD/SWAT. After risking his life at a vicious bank shootout, Blaine was recruited to CTU Los Angeles".
Blaine stands 5'8" and is in excellent physical shape making him more than fit for the challenges his new job will present. He is single though he had been for a short time engaged. It is stated that his interests include "his dog, hiking, road racing motorcycles, poker, computer games, practicing at firing range".
Blaine will find his actions in the first couple of adventures noticed and he will be moved from Los Angeles to working in the nation's capital with the FBI when his CTU boss, Alton Maxwell, is transferred to head up the Bureau's counter terrorism division.