Monroe Cooper is a private investigator who like many other PIs, searched for the missing Navy Lieutenant Brian McAllister in hopes of claiming the reward money his family was offering to find his killer.
Special Agent Timothy McGee was such a big fan of his book series, presumably based on the cases he solved, that he even had Cooper autograph one of his books for him.
Cooper was later revealed to be the one responsible for trying to kill psychic Saleena Lockhart, as part of his plan to frame McAllister's brother, Tom, to make it look as though he killed his brother. In reality, Lt. McAllister was killed in a car accident, not murdered, but the only way Cooper could claim the reward money was if he made it look as though he was killed.
It's assumed that after he was exposed and arrested, Cooper was disgraced, with both career and reputation both being ruined beyond repair.
It's also assumed that once the truth came out, his popularity took such a nosedive that he lost most of his fanbase, including McGee who was disgusted that Cooper would put an innocent person's life in danger just for the sake of money.