Some think Star Wars and Star Trek are an either/or proposition, that you can love only one or the other. Not only is it possible to love both, but here are eight actors who've crossed over to take on roles in various incarnations of each franchise.
Simon Pegg
Star Wars: Dengar, The Clone Wars / Star Trek: Scotty
Pegg recently caused a bit of fervor in the online community when it was announced that he was joining the Star Wars universe as Dengar, a bounty hunter first seen in Empire Strikes Back, in The Clone Wars. On the Star Trek side, Pegg took over the iconic role of Scotty for J.J. Abrams' reboot of the franchise, joining the starship Enterprise shortly after meeting a stranded Captain Kirk.
Dee Bradley Baker
Star Wars: Clone Troopers, The Clone Wars, multiple episodes / Star Trek: Starfleet Command III, Romulan Officer #2
We couldn't pass up Dee Bradley Baker; he hasn't been in any of the Star Trek series aside from the videogames, but he's literally the title character in The Clone Wars TV series, playing all of the clones that you see, from Rex to Cody to everyone in between. For Star Trek, he voiced Romulan Officer #2 in the Starfleet Command III videogame.
Ian Abercrombie
Star Wars: Emperor Palpatine, The Clone Wars, multiple episodes / Star Trek: Abbot / Milo, Star Trek: Voyager
Sadly, Ian Abercrombie passed away in January at the age of 78, leaving behind a long acting career that saw guest work for Star Wars: The Clone Wars, where he voiced Emperor Palpatine/Darth Sidious. He had several roles in Star Trek, where he did some voiceover work for the Star Trek: Next Generation episode "Family," and played a strict and traditional Kadi official in the episode "Someone to Watch Over Me" and Milo, a holographic resident of Fair Haven, in the episode "Spirit Folk."
Olivia d'Abo
Star Wars: Luminara Unduli, The Clone Wars / Star Trek: Amanda Rogers, Star Trek: The Next Generation
Olivia d'Abo's done some work with a number of geeky television shows over the years, doing both voice work and acting. In The Clone Wars, she's appeared in seven episodes, voicing Jedi Master Luminara Unduli. For Star Trek, she's known for her work in the Next Generation episode "True Q," playing Amanda Rogers, an unknowing member of the Q Continuum.
Brian George
Star Wars: Ki-Adi Mundi, The Clone Wars / Star Trek: Ambassador O'Zaal, Star Trek: Voyager
In Star Wars: The Clone Wars, he's voiced Jedi Master Ki-Adi-Mundi, a battlefield leader who led the Republic's elite Galactic Marines. Over on Star Trek: Voyager, he played O'Zaal, an Antarian ambassador working to coordinate peace among four civilizations.
Ron Perlman
Star Wars: Gha Nachkt, The Clone Wars / Star Trek: Viceroy, Star Trek: Nemesis
Ron Perlman shows up in a lot of places: from Hellboy to Halo, he's a distinctive person with a distinctive voice. He's showed up in both Star Wars and Star Trek.
George Takei
Star Wars: Lok Durd, The Clone Wars / Star Trek: Sulu, Star Trek: The Original Series, Various
George Takei is possibly the most notable actor to work in both franchises! Best known for his work as Sulu in Star Trek, he's acted in numerous other roles, from Heroes to Futurama. In The Clone Wars, he voiced Lok Durd, a Trade Federation commander testing a new weapons system.
Sam Witwer
Star Wars: Darth Maul, The Clone Wars/Starkiller, The Force Unleashed; Star Trek: Sloth #3, Star Trek: Enterprise
Sam Witwer is no stranger to science fiction, including the Syfy shows Battlestar Galactica and Being Human, but he's even better known for his roles in the Star Wars universe, where he voiced the main character in The Force Unleashed and, more recently, as the recently resurrected Darth Maul in the fourth season's final two episodes. Over in the Star Trek universe, he had a minor role in Star Trek Enterprise, one of the Xindi-Arboreals, as Sloth #3.