The agent has worked 'undercover' in several countries.
He went 'undercover' as a drug dealer.
an 'undercover' investigation
(..) the announcement. I have accepted a new job. Whoa! Really? Yes, I have been recruited by a top-secret agency to go undercover and save the world! You're gonna be a spy? That's right, baby! Gru's back in the game. With gadgets and weapons and cool cars. (..)2013 Despicable Me 2
(..) a master criminal. And that's where you come in. As an ex-villain, you know how a villain thinks, how a villain acts. The plan is to set you up undercover at a shop in the mall, where hopefully... Okay, I see where this is going, stuff, but no. No! (..)2013 Despicable Me 2