The following is a piece I roughed-out back in July of 2017 -- days after character actor Martin Landau passed away. It got forgotten through the passage of multiple blog posts....
Like many young people who populated the mid 1970s, I discovered Martin Landau through a television series: Space: 1999 (1975 - 1977)
As I quickly discovered while watching the show, which I did from day one, it was lame -- a young teen was disappointed. As I realized later, after seeing it in late night reruns, Mr Landau was miscast as "Commander John Koenig". I discovered a few years ago that he was highly critical of 1999. He would write comments on his scripts berating the producers and writers for what he considered to be substandard material. Landau was right. One scribbled comment I remember reading about went like this: "This makes absolutely no sense! . . . Let's get some real writers on this show."
The man had been around the actors' block for some time by this point; working with directors such as Alfred Hitchcock and Lewis Milestone. Landau enjoyed great success as "Rollin Hand", one of the key IMF agents on television's popular dramatic series Mission: Impossible (CBS, 1966 - 1973). It was because of that series' name-brand quality that he was cast as series lead in Space: 1999. (Editorial: Hiring Landau and his then wife Barbara Bain was a big mistake. But they were 'names'; which, as it turned out, did not help the series succeed -- over and above some interesting visual stylings. As 1999 producer Sylvia Anderson said in an interview, Martin Landau "is" an excellent character actor, but not a leading man. Trivia: She wanted to cast Robert Culp.)
If one wants to stick with SF episodic television featuring the actor in guest-shot roles, watch the Outer Limits episodes "The Bellaro Shield" and "The Man Who Was Never Born".
Landau was memorable -- I would say "terrific" -- as "Leonard", implied lover of James Mason's Phillip Vandamm in Alfred Hitchcock's 1959 classic North by Northwest.
More films to check out: the underrated Tucker: The Man and His Dream (1988), the essential Ed Wood (1994), and the superb Crimes and Misdemeanors (1989).
Television episodes to check out: "Devil's Planet" and "The Bringers of Wonder".