Jonathan "Prophet" Simms is an agent of the BAU's fictional Red Cell team, the protagonists of the spin-off Criminal Minds: Suspect Behavior. He and the rest of the team first appeared in The Fight.
Background
Simms was a former convict who had spent six years, three months and four days in the San Quentin prison in California for killing a child molester. It was unspecified whether he had served time in other prisons as well. It was in prison that he got his nickname, "Prophet", though it is unknown as to how or why he got it. Not much else has been revealed about him, except that he intended to make amends for past sins, using his street-smart edge and Zen-like ways.
The Fight
Simms was paired up with Rossi during the investigation of a series of murders in San Francisco. Having figured out that the unsub had been to prison, they went to San Quentin to talk to Nelson G., an old friend of Simms "from back in the dark days", and gave him the profile hoping the inmate could give them the identity, or at least some clue about the UnSub. In the end, it was the information they got from Nelson what would lead both teams to zero in the UnSub's name.