The First Star Trek Actor To Play A Vulcan, Klingon, And Romulan
While it's unusual, it's not rare for an actor to appear in the same television show as two separate characters. Sometimes this will happen when the first character is more of an extra, without a name or many speaking lines. A producer or showrunner will see the dailies and really like the person's look or their acting and want them to come back in a larger role. Another example is how a show that is on the air for many years may have an actor in a specific role in Season 2, and then they come back as an entirely different character in Season 8. Why not? It's likely that no one remembers their previous character anymore, anyway.
The ever-expanding "Star Trek" franchise has had quite a few actors portray different characters across its universe of many television shows and films. For example, Jeffrey Combs played eight different characters in "Star Trek: Deep Space Nine, "Star Trek: Voyager," and "Star Trek: Enterprise," among them an Andorian, a Weyoun, and a Ferengi (via Star Trek, CBS). But one other actor also played multiple roles in the "Star Trek" universe, even though he's probably best remembered as the father of Spock (Leonard Nimoy).
Mark Lenard played three different characters in the Star Trek universe
Mark Lenard's first appearance as Spock's father Sarek is in Season 2, Episode 10 of the original "Star Trek" series, titled "Journey to Babel." He would go on to also play Sarek in "Star Trek: The Animated Series," "Star Trek: The Next Generation," and the third, fourth, and sixth "Star Trek" films (via IMDb). But few fans realize that Lenard's first role in the franchise wasn't as a Vulcan, but rather, as the first major Romulan character in the show, playing a hostile commander in Episode 14 of the first season.
When "Star Trek: The Motion Picture" was released in 1979, Lenard could've easily played Spock's father again, but instead, the creators brought him on in the role of a Klingon captain. While it's not as notable a role, it makes Lenard one of the only "Star Trek" actors to play three unique roles of different alien species within the iconic sci-fi universe. Throughout his long career, Lenard always embraced the "Star Trek" franchise and its legacy, not only narrating the video game "Star Trek Omnipedia" in 1995 but also writing a "Star Trek: Deep Space Nine" comic book called "Blood & Honor," which was published shortly before Lenard's death in 1996 (via Goodreads).