Diana Muldaur - most famous for the season long appearance as Dr. Pulaski on TNG - was a main guest star on two different TOS episodes (as two different characters, Anne Mulhall in Return to Tomorrow and Miranda Jones in Is There in Truth No Beauty). All three characters were memorable in different ways, though I've always thought Pulaski deserved more development than she got as a major character. But Lt. Cmdr. Mulhall in particular is one of my favorite guest characters in the franchise. The chemistry she had with Kirk was incredible and I wish we lived in an alternate universe where Muldaur was allowed to join the main cast on a weekly basis as Anne Mulhall. She would've brought a different and fantastic dynamic to the bridge.
But TNG reprised the largest number of TOS characters. Spock, Sarek, Scotty, Kirk. Plus, Terry O'Quinn, Ronny Cox, Paul Sorvino, James Cromwell, Ray Walston, Matt Frewer, Saul Rubineck, David Ogden Stiers, Famke Janssen, Ashley Judd, Paul Winfield, & of course, both Kelsey Grammer & Bebe Neuwirth lol. I'd say they got their fair share of noted performers
How about some love for Leland Orser. He appeared twice on DS9. He helped the Xindi on ENT. And his turn as a bitter hologram on VOY was particularly good.
Unless I missed it, I don’t think anyone mentioned the brilliant Mark Lenard. Absolutely amazing as the Romulan Commander in Balance of Terror, and even better in each of his appearances as Sarek.
Some of these (Worf and Troi in particular) are the result of spellchecks or speech-to-text programs.
Don't get me started on "Kahn," which I've actually seen in published articles. And our local newspaper spelled Uhura "Uhuru" just this week. And then there's Chekov versus "Chekhov."
Funny, because that's the actual correct spelling. Star Trek introduced the feminine version to the language.
If my autocorrect doesn't stop replacing Troi with trio, & Worf with word. I'm going to smash it someday, just like Word would