He is perhaps best known to science fiction fans for appearing in two separate films and a two part episode of the Star Trek franchise: Star Trek V: The Final Frontier, Star Trek VI: The Undiscovered Country and the Star Trek: The Next Generation Season Six episodes "Chain of Command, Parts I and II".
He has also made several appearances in Doctor Who media, most notably as an alternate Third Doctor in Doctor Who in the stories Sympathy for the Devil (2003) and Masters of War (2008). He's also appeared in other Doctor Who stories, Circular Time (2007) and Empathy Games (2008). Also appearing in the Doctor Who spin-off series Bernice Summerfield in the story The Adventure of the Diogenes Damsel (2008).
He also appeared in the Doctor Who animated story Dreamland (2009), and appeared as Russian Professor Grisenko in the eighth episode of series seven, aired in April 2013.