He had a role in Star Trek: Voyager in 2000, making him one of the very few actors to appear in both Doctor Who and Star Trek. At the time of his death, he was the oldest-living actor from both franchises.
In 1966, he starred in the six-part Southern TV adaptation of T.H. White's adventure novel The Master, playing the 157-year-old titular character, who has the power of hypnosis and thought-transference, with aspirations of world domination.
In his final years, he took to painting, and celebrated his 100th birthday with an exhibition of his own works.
He passed away after suffering congestive heart failure.
He was the second person, and first male, associated with Doctor Who to reach the age of 100, after actress Zohra Sehgal.