Felix Leiter is an agent with the CIA.
Most of the time he is. When we think about him, it is in that capacity though life will throw him a very nasty curveball and he will be retired on full disability. That does not mean, though, he is out completely and will on occassion be called back for this job or that.
We know very little about Leiter from the recorded adventures. We can read that he has "a mop of straw-coloured hair" that gave him a look far younger than his eyes would give. The impression is there that he is rather tall and lanky further making him appear almost coltish. The fact, however, that a seasoned hard-as-a-rock agent like James Bond would treat him as an equal and later as a very close friend show that Leiter, for all his youthful appearances, is a man who has been around the block more than once.
Things we do know about him:
1. He is on hand to provide much needed resources for Bond on several occasions (Casino Royale, Goldfinger, and such)
2. He is a big fan of Jazz and in his younger days even wrote a few articles on the subject
2. He will suffer a horrendous injury thanks to a villain's shark and not let it stop him.
3. He will be married a couple of times and help create a beautiful daughter named Cedar who would, when she became an agent with the Agency like her father, attract the roving eye of his best friend (rather unsporting of Bond, IMHO).
4. Shows that he is not only capable of working on his own but is also a team player, willing to take the second chair when needed.
Naturally since Felix Leiter is first and foremost a compatriot of 007, for more information check out .