(written from a Production point of view)
In 1995, Riordan starred as Captain Zoom in the TV movie The Adventures of Captain Zoom in Outer Space (in which Ron Perlman and Nichelle Nichols also appeared). A co-writer and supervising producer of that production was David A. Goodman, who later described Riordan as a "very good actor." (ENT: "Judgment" audio commentary podcast)
He also voiced additional voices in Star Wars: The Old Republic (with D.C. Douglas, Francis Guinan, Armin Shimerman, Charles Dennis, Nolan North, Maury Sterling, Gary Schwartz, Tasia Valenza, Joseph Gatt, Robert Pine, George Coe, Alan Shearman, Alec Newman, Armand Schultz, Brian George, Bumper Robinson, Christopher Neame, Clive Revill, Emily Bergl, Fred Tatasciore, Greg Ellis, Jason Marsden, Keith Szarabajka, Larry Cedar, Michelle C. Bonilla, Miriam Flynn, Paul Eiding, Robin Atkin Downes, Sherman Howard, Wayne Grace, and S.A. Templeman). In 2019, he voiced a major supporting character in the game Days Gone (alongside Sam Witwer and Phil Morris).