Garry Marshall, who plays Oscar's father, Walter, is the creator of the original series, The Odd Couple (1970). He also served as consultant on this version. On the wall in Oscar's apartment is a photo of Matthew Perry (Oscar), Thomas Lennon (Felix), and Garry as tribute to him.
Garry Marshall guest stars as Oscar Madison's (Matthew Perry) father, named Walter Madison. The first name Walter is an homage to actor Walter Matthau, who originated the role of Oscar Madison in the 1967 movie, The Odd Couple (1968).
This was Garry Marshall's final screen appearance before his death a few months after this aired.
Garry Marshall was the Executive Producer of the original Odd Couple series.