Mark Lenard, best known for his role as Sarek, Spock's father, was the first actor to play a member of all three of the major alien races: Vulcan, Romulan (in the episode "Balance of Terror"), and Klingon (the commander of the Klingon attack group at the beginning of Star Trek: The Motion Picture (1979)).
James Doohan ("Scotty") lost his right middle finger during WWII. Most of his scenes are shot to hide it. In scenes with a close-up view of Scotty's hands (operating the transporter for example) someone else's hands were always used. However, it is noticeable on a few rare occasions. The most obvious example is "The Trouble With Tribbles" when Scotty comes into the Rec Room with his arms filled with Tribbles. Take a close look at his hands. You can clearly see he's missing a finger.
As a Sub-Commander serving the Vulcan High Command, T'Pol was stationed aboard the original Enterprise in April 2151, as an observer to Captain Jonathan Archer and his crew, who the High Command insisted were not ready for interstellar space exploration. After the success of the Enterprise's initial mission led to the vessel being given an extended exploration mandate, T'Pol requested to stay aboard as science officer.