Nick Munroe

This Siren takes many forms, but he appears as Nick Monroe to Sam and Dean.

Background
He appears to Sam and Dean as a FBI agent also working the same case. Sam and Dean splilt up and Dean goes with Nick to the strip club. There they get close and Dean realizes that Nick is not so up tight like most feds. Dean is further impressed by how much he has in common with Nick. Nick mentions to Dean that at each crime scene there was a flower found; the same flower located in Dr. Cara's office.

Later on Dean calls Nick to help him out on a stake out. Dean also tell Nick that Cara is drugging her victims as they share a drink. During this time, Dean gets infected with the siren's drug, and Nick reveals himself as the siren. Dean is completely under his control. So they return to the motel room, and Nick reveals the meaning behind his form. Dean didn't really want some chick, but a little brother that looks up to him and trusts him. Nick drugs Sam and makes the two fight for him. Nick is killed when Bobby arrives and throws the knife at him.