I'll admit that as a kid, I didn't find Ms. Bain to be particularly pretty, and thought she was "old." But, hey, I was a stupid kid. In later years, especially after watching her on the early seasons of Mission: Impossible, I came to appreciate her finely-sculpted, fashion model features and her genuinely impressive dramatic skills. It's a shame that the producers of Space: 1999 seemed to demand from the cast a cold, unemotional (okay, "wooden") acting style reminiscent - like much of the show - of Stanley Kubrick's 2001: A Space Odyssey (of course, in Year Two, the acting style would trend too far the other way...), because Ms. Bain is an actress of considerable range and warmth, and it would have been nice to see more of that talent evident on the show.
Born Millicent Fogel in Chicago in 1931, Bain was a successful dancer and model before getting into acting. Bain co-starred with husband Martin Landau not only on Space: 1999, but the aforementioned Mission: Impossible, as well, for which she became the first person to win three consecutive Emmy Awards for "Best Actress." In recent years, she has contributed much of her time to various charities.
ADDENDUM 5/4/11: Here's a LINK to a recent interview with Ms. Bain!