An undercover investigator,undercover detective or undercover agent is a person who conducts an undercover operation into those suspected of criminal activity. The undercover investigator will often infiltrate a suspected criminal group and disguise themselves as a person interested in goods or services with the goal of gaining information and evidence of a suspect. The tools of an undercover investigator often include a hidden camera called a body camera or recorder that they wear concealed under their clothing to record all the evidence.

Undercover operations can take months or even years so it is imperative that the true identity of the undercover investigator remains concealed as this can be a dangerous job. Undercover investigators are also used to investigate employees for bogus sick leave, abuse of fellow colleagues and espionage.