10 Actors with the Most Star Trek Roles
5+ credits: Taibak (TNG: "The Mind's Eye"), Cardassian overseer, uncredited but with dialogue (DS9: "The Homecoming"), Ornithar (DS9: "The Search I"), Koval (DS9: "Inter Arma Enim Silent Leges"), Abaddon (VOY: "Alice"), Silik (ENT).
John Fleck could be seen in increasingly important roles, culminating in the recurring character of Silik in Enterprise.
9John Kenton Shull
6 credits: Klingon actor (TNG: "Firstborn"), Bajoran security deputy (DS9: "Shakaar"), Hanonian medicine man (VOY: "Basics II"), K'Temang (DS9: "Return to Grace"), Brok'tan (VOY: "Barge of the Dead"), Nocona (VOY: "Homestead").
John Kenton Shull can be seen in six credited roles altogether.
8Paul S. Eckstein
6 credits: Limara'Son (DS9: "Rocks and Shoals"), Young Hirogen (VOY: "The Killing Game I+II"), Supervisor Yost (VOY: "Gravity"), Jem'Hadar guard (DS9: "The Dogs of War"), New Alpha Hirogen (VOY: "Flesh and Blood"), Morak (VOY: "Prophecy).
Paul S. Eckstein too is credited in all six of his Trek roles but remains unnamed in some of them.
6 credits: Galt (TOS: "The Gamesters of Triskelion"), Tumek (DS9: "The House of Quark", "Looking for par'Mach in All the Wrong Places"), Cardassian informant (DS9: "Improbable Cause"), Son'a officer ("Star Trek: Insurrection"), Vulcan master (VOY: "Gravity"), Suliban doctor (ENT: "Broken Bow").
Joseph Ruskin (1924-2013) is one of the few veteran actors who appeared both in TOS and in the second generation of Trek, and the one with the most different characters (ahead of Clint Howard).
6 credits: Mirok (TNG: "The Next Phase"), Train engineer (TNG: "Emergence"), Viorsa (VOY: "The Thaw"), Kira Taban (DS9: "Ties of Blood and Water", "Wrongs Darker Than Death or Night"), Tos (ENT: "Broken Bow"), unnamed alien (ENT: "Harbinger"). Honorable mention: Kopache could be seen on the bridge of the Enterprise-B in "Generations" in an uncredited small role.
Thomas Kopache is not such a well-known name in the fandom, but the mere fact that he appeared six times on Star Trek is impressive. Yet, there are still four other actors with six roles that were more notable.
6 credits: Nazi officer "Kapitan" (VOY: "The Killing Game I+II"), One (VOY: "Drone"), Vornar (DS9: "Tacking Into the Wind"), Mestral (ENT: "Carbon Creek"), Nazi officer (ENT: "Zero Hour"), Nazi SS officer (ENT: "Storm Front").
Paul Boehmer appeared as six different characters, among whom at least One from VOY: "Drone" is very memorable, but he also has the questionable honor of playing the most Nazi roles on Trek.
6 credits: Scholar/Artist in Riva's chorus (TNG: "Loud as a Whisper"), Ah-Kel and Ro-Kel (DS9: "Vortex"), Silaran Prin (DS9: "The Darkness and the Light"), Kir (VOY: "Counterpoint"), Trena'L (ENT: "Unexpected"), Degra (ENT).
Randy Oglesby played five guest characters until he got his first recurring role on Star Trek as the Xindi-Primate Degra, which earns him the overall fourth place and the third place among the actors with six roles.
6 credits: Vulcan captain (DS9: "Emissary"), Martok (DS9), Laas (DS9: "Chimera"), Hirogen fighter (VOY: "Tsunkatse"), Kolos (ENT: "Judgment"), Klingon captain (ENT: "Borderland"). Hertzler also voiced the Drookmani captain in LOW: "Terminal Provocations" and "A Mathematically Perfect Redemption".
Among the various actors with six different parts on this list, J.G. Hertzler is the runner-up. He has an additional voice acting credit and he played General Martok after all!
6 credits: Tiron (DS9: "Meridian"), Brunt (DS9), Weyoun (DS9), Penk (VOY: "Tsunkatse"), Thy'lek Shran (ENT), Krem (ENT: "Acquisition"). Honorable mention: His voice for the evil computer AGIMUS in LOW: "Where Pleasant Fountains Lie" and "A Mathematically Perfect Redemption".
Jeffrey Combs, like J.G. Hertzler, appeared in six different roles and voiced one animated character. I put Combs ahead of Hertzler because he had three recurring parts and appeared in overall more episodes.
11 credits: Captain Korris (TNG: "Heart of Glory"), Gul Danar (DS9: "Past Prologue"), Telek R'Mor (VOY: "Eye of the Needle"), Seskal (DS9: "When It Rains...", "The Dogs of War"), Two of Nine aka Lansor (VOY: "Survival Instinct"), Vidiian captain (VOY: "Fury"), Alpha Hirogen (VOY: "Flesh and Blood"), Korath (VOY: "Endgame"), Admiral Forrest (ENT), Klingon captain (ENT: "Sleeping Dogs"), Kreetassan captain (ENT: "Vox Sola", "A Night in Sickbay").
Wow. Now that is impressive! With 11 appearances, Vaughn Armstrong easily (and not unexpectedly) tops the list of the actors with the most different Trek parts. An unsurpassable record?
Other actors with appearances as 5 different characters:
- Rick Worthy: Automated Unit 3947 and Automated Commander 122, two distinct aliens that are much like twins though (VOY: "Prototype"), Kornan (DS9: "Soldiers of the Empire"), Ellora officer ("Star Trek: Insurrection"), Crewman Lessing (VOY: "Equinox I+II"), Jannar (ENT)
- Steven Dennis: Night Alien, technically even 2 of them (VOY: "Night"), Fennim (VOY: "Think Tank"), Onquanii (VOY: "Warhead"), Crewman Thompson (VOY: "Equinox I+II"), Tholos (ENT: "The Andorian Incident", "Shadows of P'Jem")
- Gregory Itzin: Ilon Tandro (DS9: "Dax"), Hain (DS9: "Who Mourns for Morn?"), Dr. Dysek (VOY: "Critical Care"), Sopek (ENT: "Shadows of P'Jem"), Admiral Black (ENT: "In a Mirror, Darkly II")
- Lee Arenberg: Gral (DS9: "The Nagus"), Prak (TNG: "Force of Nature"), Bok (TNG: "Bloodlines"), Pelk (VOY: "Juggernaut"), Gral (ENT: "Babel One", "United"), notably with three Ferengi parts and as two distinct characters both named "Gral"
- Eric Pierpoint: Voval (TNG: "Liaisons"), Captain Sanders (DS9: "For the Uniform"), Kortar (VOY: "Barge of the Dead"), Shiraht (ENT: "Rogue Planet"), Harris (ENT: "Affliction", "Divergence", "Demons", "Terra Prime")
- Marc Alaimo: Selay delegate, uncredited but with dialogue (TNG: "Lonely Among Us"), Tebok (TNG: "The Neutral Zone"), Macet (TNG: "The Wounded"), Frederick La Rouque (TNG: "Time's Arrow I"), Gul Dukat (DS9)
- Brian Thompson: Lieutenant Klag (TNG: "A Matter Of Honor"), Inglatu (DS9: "Rules of Acquisition"), Toman'torax (DS9: "To the Death"), Admiral Valdore (ENT: "Babel One", "United", "The Aenar"), also uncredited as a Klingon helm officer ("Star Trek Generations")
- Brent Spiner (if we are generous): Data/Lore/B-4/M-5-10 plus four Soongs, and counting
More honorable mentions:
- Actors with appearances as 4 different characters (finally including some women): Armin Shimerman, James Sloyan, James Horan, Suzie Plakson, James Cromwell, Clint Howard, Kurtwood Smith, Carolyn Seymour, Peter Slutsker, Phil Morris, John Schuck, Bruce French, Christopher Shea, Steve Rankin, Michael Ensign, Leland Orser, Christopher Collins, Tim de Zarn, Alexander Enberg
- TOS stand-ins and stunt performers with many (usually uncredited) roles: Frank da Vinci, Paul Baxley, William Blackburn, Vince Deadrick, Jay Jones, Jeannie Malone
- TNG/DS9/VOY/ENT background actors with many (usually uncredited) roles: Patricia Tallman, Elle Alexander, Dieter Hornemann, Cathy DeBuono, David B. Levinson, Shepard Ross, Guy Vardaman
- Actors who voiced countless characters (animated or computers): Majel Barrett, James Doohan, Nichelle Nichols
I consulted many sources and other people's listings of recurring actors, but only Memory Alpha provided reliable data.