Robert Picardo was on Voyager and SG1 (in several episodes)
Brian
He also did a guest shot on Star Trek: DS9, as the engineer in a corps of Starfleet soldiers in “The Siege of AR-558.”
Andreas Katsulas, who played G’Kar on Bablyon 5, appeared in Star Trek: TNG as the Romulan Commander Tomalak in several episodes, and apparently was also a Vissian captain in Enterprise.
I have a few more if we’re including movies. Can we get an official word on that from the OP?
Ted Raimi had recurring roles on “SeaQuest DSV,” “Hercules” and “Xena,” and one-shot roles on “Alien Nation” and “Odyssey 5.”
John de Lancie was on Star Trek:TNG, DS9, and Voyager as Q, and was also on Stargate SG-1 as Col. Simmons.
Edit: Also, if you include video games, Grace Park and the girl who plays six on BSG (Can’t believe I can’t remember her name!) are in Command & Conqueror 3
Jonathan Harris was in LOST IN SPACE and SPACE ACADEMY
James Doohan was In STAR TREK and JASON OF STAR COMMAND
He was also a regular on the fantasy-western series “Legend,” which starred Richard Dean Anderson.
John Colicos played Kor on Star Trek TOS (and DS9), and Baltar on Battlestar Galactica TOS.
I was thinking of TV in particular, mostly because thats when I go “hey, I’ve seen that person before in another SF show”
I’d prefer at least one show to be semi current, but thats not an absolute rule.
(Bill Shatner in Star Trek and Twilight Zone is an older example)
And bonus points for more regular appearances (take the product of how many episodes they appear in to get the bonus points. 5 episodes of show A and 20 episodes of show B equals 100 bonus points)
Brian
Also from the X-Files:
David Duchovny was an android (cant remember the correct term atm) in the most excellent Space: Above & Beyond, and most of the cast from Space went on to guest star in The X-Files too.
Also on Sanctuary: David Hewlett & Paul McGillion (Stargate: Atlantis) and Leah Cairns (BSG).
also “The Starlost” as Oro 2 episodes, The Alien Oro (1973) - The Return of Oro (1974) and if “I Spy” counts 1 episode.
I think I found the guy to beat, Armin Shimerman*****.
From his IMDb bio;
Ben 10 - Slix Thigma - 1 episode,
Invasion - Josh Breims - 2 episodes,
Justice League - Dr. Milo - 1 episode,
Evil Con Carne - General Skarr - 3 episodes,
The Tick - The Terror -1 episode,
Tremors - Cecil Carr -1 episode,
Charmed - The Wizard - 1 episode,
The Invisible Man - Augustin Gaither - 3 episodes,
Buffy the Vampire Slayer - Principal Snyder -19 episodes,
Star Trek: Deep Space Nine - Quark - 173 episodes,
Sliders - Shape-Shifting Guard - 1 episode,
The Lost World - Professor George Edward Challenger,
Stargate SG-1 - Anteaus - 1 episode,
Star Trek: Voyager - Quark - 1 episode,
Star Trek: The Next Generation - DaiMon Bractor / Quark / Gift-Box Face / Letek - 4 episodes,
Alien Nation - Cyril Roman - 1 episode,
Beauty and the Beast" - Pascal -11 episodes.
CMC fnord!
Gina Torres was a regular on Cleopatra 2525 and Firefly. She also guest starred on episodes of Angel, Hercules, and Xena - as well as Alias, Justice League, and Profiler (series which some people might call SF).
Since Xena and Hercules have been included- Lucy Lawless in Battlestar Galactica and Kevin Sorbo in Andromeda.
Morena Baccarin (Inara on Firefly) has also had a recurring guest role on Stargate: SG-1.
Dean Stockwell, who played Al on* Quantum Leap*, has a recurring role as “Father” Cavill on BSG.
No, there’s John Billingsley (Dr. Phlox). 98 Episodes of Enterprise, 13 episodes of The Others, and guest roles on Angel, Stargate SG-1, G vs. E, The X Files, The Pretender (twice), Ghost Whisperer and Roswell (as himself).
I think we may have a winner.
Both William Shatner and Leonard Nemoy did epsoides of the Twilight Zone before ST.
And The Outer Limits.
Daniel Dae Kim also played an attorney with Wolfram & Hart. (Angel.)
Jonathan Woodward famously appeared in Angel, Buffy & Firefly. Such a nice guy–but there’s always something wrong with him. (His roles, not himself.)
Gary Lockwood played Kirk’s pal Lt. Cmdr. Gary Mitchell in TOS “Where No Man Has Gone Before,” doomed astronaut Frank Poole in 2001: A Space Odyssey, and later appeared in TV’s Dark Skies, Macgyver, and the original Mission: Impossible.
He also appeared in the semi-mocumentary Trekkies. 