Walter Matthau played the original Oscar Madison in the film version of The Odd Couple (1968), while Tony Randall played the part of Felix Unger in the classic TV series The Odd Couple (1970), upon which it was based. This was (unfortunately) the only time the 2 men worked together.
Director Morton DaCosta previously directed Robert Preston ("Steve Blair") in "The Music Man," both on the Broadway stage and in the film version. Preston played a con man there as well.