In the original Los Angeles-based episodes of Mathnet, the chief, Thad Green, was played by James Earl Jones. Despite a change in chiefs with the move to New York City, Jones made one appearance via phone in a season 4 episode.
Gary Owens, alias the title character in Roger Ramjet, as Lt. Dirk Niblick of the Math Brigade. (Furthermore, like Roger Ramjet, the Dirk Niblick segments were written by Jim Thurman and animated by Fred Crippen.)
Jim Thurman as Glitch in the Mathman segments and as supporting characters in the Dirk Niblick segments.
Keep Circulating the Tapes: The series has not been rerun since the early 2000s, when it was rerun on Noggin, and there are currently no DVD releases planned. Domestic recordings do exist of many episodes, and they sometimes show up on YouTube, but they are nowhere near exhaustive, and quality varies widely.
Too Soon: An exception - not long after the September 11 attacks, Noggin aired an unedited episode in which George Frankly casually discussed having dinner at Windows on the World at the World Trade Center.
Written-In Infirmity: The likely reason Kate Monday is holed up in the "Mathnet" episode "The View from the Rear Terrace".