Wayne once worked as a black operations agent until the shooting-related death of the wife of a Ukrainian mobster boss. He fled to America and got a job as a security guard at the Springfield Nuclear Power Plant, where he met Homer, who wanted to befriend him. Wayne kept to himself at first, but that changed when he stopped Snake Jailbird from robbing Moe's Tavern. The news crew meets up with him at work, where he is being rewarded for his heroism. Troubles from the past cost him his job when he attacks Mr. Burns after having a painful flashback as he is being awarded. To which Homer allows him to stay in his house. After much talk, Wayne starts to open up about his past, and admits to the Mafia being on his case. Later, the widowed mobster finds the video of Wayne attacking Mr. Burns and goes to Springfield.
When the mobster arrives, he finds Homer washing the dogs' droppings on the lawn; he asks Homer about Wayne and ends up kidnapping Homer when they find out that Homer is Wayne's friend. When Homer gets kidnapped by the Ukrainian mob, Wayne knows he's the only one who can save him. Wayne tracks the group down in an ice hockey arena thanks to the GPS system Homer swallowed (since they were left out in a bowl). Wayne finds Homer trapped underneath the ice in the arena. After confronting the mob and taking out all the mobsters, Wayne freed Homer. Wayne decides to leave Springfield, claiming he can't stay in one place, but not before bumping fists with Homer. However, Marge suggests a job where "a sadistic man with government experience can feel right at home": the DMV, where Wayne remembered a time when he was imprisoned in North Korea, and was also forced to write a play about North Korean leader, Kim Jong-il.
He later appeared in The Simpsons: Tapped Out as a character during the Secret Agent 2017 Event.
Wayne Slater is one of the few characters to actually show a remarkable physicality & fitness, as well as top-level martial artistic skills, marksmanship skills & espionage skills. He is also extremely resourceful as he created his own unique flame-t shirt gun to fight the Ukrainian mobsters.
He seems to have an almost sociopathic personality and rarely smiles, but he does show compassion with the Simpson family, whom he considers his friends.
Also, he seems to suffer PTSD (Post Traumatic Stress Disorder) regarding traumatic experiences of his past missions, which it's triggered by any thing or action in relation with his past memories and it causes him to panic and attack any person near him who triggered it and even had nightmares about his past traumas while staying with the Simpsons.