Joe Wylee is a police detective who's engaged to Dale Arden. In the episode "Secrets and Lies", his police captain suspends him, thinking that he's unfit to be a cop.
In the episode "Possession", he travels to Mongo and for the first time meets Ming. Joe agrees, by the end of the episode, that the fewer people who know about Mongo the better.
At the end of the episode "Ebb and Flow", Joe sacrifices himself to complete the destruction of Ming's aqueduct.