Walt is first seen in "Boys' Night", when neither Phil nor Claire are willing to go to his house to retrieve their baseball, despite the fact that it was their only one. The two seem scared and intimidated by Walt, and Claire claims that if "Freddy Krueger and Hannibal Lecter had a love child, he would be scared of Walt Kleezak". Phil states that while he does not have a bad word to say about anyone, he states "Mr Kleezak is not a nice person". Later in the episode, Walt comes over to the Dunphy's house with onions, as a gift, and states that he will not harm Luke. The family and Walt latter become friends, largely through Luke and Walt's relationship.
Later in "The Last Walt", Walt suffered a heart attack and later died.