Andy Umberger
Andy Umberger played D'Hoffryn in four episodes of Buffy the Vampire Slayer and guest starred as Dr. Ronald Miltzer in the Angel episode "I Fall to Pieces". He also appears as the Captain of the I.A.V. Dortmunder in the pilot episode of Firefly.
Along with Jeff Ricketts, Carlos Jacott, Bob Fimiani, and Jonathan M. Woodward, he is one of only five actors to appear in the first three series created by Joss Whedon.