Chandra Smith is an agent for an unnamed secret agency.
He specifically works for Mr. Ames. Mr. Ames' connections are little known, except that it is said he was one of the few people who could get in to see the President whenever he wanted. Mr. Ames is also powerful enough to get men transferred when and where he wants, just by mentioning it.
Smith is also an officer in the American military. While it is not specifically mentioned which branch, it seems to be one of the Special Forces. He holds the rank of Lieutenant when the series begins but is almost immediately promoted to Captain and possibly later to Major. Whatever service he belongs to, he is actually assigned to work directly for Mr. Ames.
Smith is the son of an American father and an Indian mother, from whom he learned to speak Hindi along with several dialects thereto as well as a good deal of the history of that sub-continent. His skin coloring allows him to fit in numerous areas of Asia and the Middle East, making him an excellent agent for blending in. Coupled with his knowledge of languages and his ability to handle himself in tight situations, it is easy to see why he gets promoted easily.
Having worked for Mr. Ames for a couple of years at the start of the series, Smith, who is probably in his late 20's, is accustomed to hard missions and hard fighting but he is by no means anxious to get involved in a brawl without a good reason. He had learned long before the pain that comes from one, whether winning or not. But once pushed into a fight, he knew winning was always better.