Belle Jones is a part-time agent for the CIA.
She will be. After they capture her and let her know that a black site had a tiny room all ready for her; one she would never leave except for an hour a day in a tiny courtyard, she will agree to work for them. Actually the whole reason she let (and that is the operative word) herself get captured was so someone like them in the alphabet community would make such an offer (to work for them, not to get locked up). Things on her own were getting a little dicey so having some backup finally seemed advisable.
"I don't know what it says about me that my biggest accomplishments in life involved hunting down and killing people." That is her opening line to us in a prologue to the first recorded adventure. She also tell us that the name mentioned above was not her real one but a nomme de guerre that she had intended to dump once she got "entrenched" in the shadowy world of terrorists and those who fund them.
"Early in my career I came across an Algerian terror cell that had a warning about me on their dining room wall with my picture and the term Belle Dangereuse, with a red bolded FATALE under it. That was fine by me; let them know me as the deadly woman, the dangerous beauty, the belle fatale. After all: that is exactly what I am."
Her motivation for her actions was straightforward. "Bin Laden and Al-Zahrani killed my mother in 9/11. His spawn killed someone else in Afghanistan [her brother serving there]. I want him dead. I wanted his entire network dead. But if you pull a weed you gotta get the roots."
Alexis Lisbeth Johnston is the name she likely was born with but it has been so many years and so much has happened, she seems to feel a lot more comfortable with Belle Jones. She says she has a "slim body" with long brown hair. She also says that she is not a fan of being handcuffed or being rough-housed and she has proven both statements, to the chagrin of several much larger and stronger men.
After she sets herself up to be captured at the beginning of the series, a CIA interrogator remarks to her on her, "You were an adequate spy. Really excellent fighting skills; you learn languages like people learn to breathe; you keep cool and you're one hell of a shot. In a way, you're a con artist, a black widow and a James Bond all in one. And you're American. Interpol wants you for a half a dozen crimes, but I don't think you're really a criminal at heart. I think you're more than that." That is all to the positive. On the other side, he lets her know, "You're under arrest for espionage, murder, arson, drugs charges, international violations, we can go on."
- Said to a Marine guard watching warily over her, "I like Marines; they don't whine. The military wouldn't have taken me. I'm kinda psycho."