Martin Landau...

Martin Landau was indeed a major player in the series “Mission: Impossible” and was a big factor in its success. Landau and then wife Barbara Bain were regulars in the first three seasons of seven total. Landau was nominated for an Emmy for each of his three seasons. Bain was also nominated three times and won one of them. The show ran from 1966 to 1973. Of the actors who were regular or semi-regular cast members, we have lost:

Steven Hill (team leader in season one)
Peter Graves
Greg Morris
Leonard Nimoy
Bob Johnson (the voice on the self-destructing tape: “Good morning, Mr. Phelps.”)
And, now, Martin Landau

A surprising number of regulars and semi-regulars are still with us, including:

Barbara Bain
Peter Lupus (all 7 seasons. Had a cult following as the Man Who Never Talks. Actually, he did have a line or two in most shows but mainly he, litterally, did all the heavy lifting)
Lynda Day George (last two seasons)