Magus Crayle is an agent with the CIA.
That is what people tell him and why would they lie? He wouldn't know, at least when we first meet him, because he suffers from amnesia, having been in a very nasty car accident from which he barely survived, and cannot remember for himself. Which is why he is assigned a couple of people to watch over him, one from the FBI and one a private investigator. Remembering, though, is going to take time and there are people out there who definitely do not want his memory to come back.
In his own words, "My name is Magus Crayle. I know that because I have been told. I have awakened to a world I do not remember. I look about at my surroundings as I suppose does a baby, but a baby, I am not. My private investigator has recovered that I was a government functionary - perhaps a mathematician. Also my university. But no parents, siblings, wife, children, friends - nothing. I have myself discovered familiarity with an Oriental philosophy ... and an artist, Yao-wu. I recall one rock and roll song. I am a grown man of ... I don'’t know the years. There are healed bruises and gashes on my body. I am rehabilitating from a near-fatal automobile crash in which I should have died. ... I am Magus Crayle."
As those memories that elude Crayle so much start to come back, he sometimes learns and sometimes remembers he was once associated with the CIA and that he was a mathematician. Except there are probably not many math experts who have the abilities that Crayle learns he has. When nasty people come to try and finish the job of eliminating him, he is able to use what lay about to remove them. This is understandably confusing. As he thinks, "Reconciling those lethal survival skills to his government-job title of mathematician and foremost world-conquest planner would take time."
It is that 'world-conquest planner' that forms the crux for all the adventures that Crayle is forced into. Before his accident, which of course was no accident, he had involved in coming up with a sequence of events that would transform governments like China, Russia, France, the U.K., and the U.S. into wildly different states - a return of sorts to the old ways. Kings and Emperors and autocracies controlled ultimately by the super secret Illumine.