Just found out, although it happened some time ago.
http://starbulletin.com/2002/02/17/news/story9.html
One (sorta) interesting thing is that when “The Cage” was originally shot, Wyllie’s character was referred to as “Magistrate,” never “Keeper.” That didn’t happen until it was re-edited into the two-parter “The Menagerie,” which would become the only two-parter in the series.
A year earlier, “Lost in Space” had a two-parter–the only two-parter of ther series–called “The Keeper,” which was about space traveler (Michael Rennie, long-time friend of Jonathon Harris) who collected a menagerie.
Probably just coincidences, but just thought I’d bring it up.
At first I thought you meant the actress who played Vina, Susan Oliver, who I’d just seen in one of Sci-fi-channels Twilight Zone marathon. Now I’m bummed to read that she died in 1990 (Cancer).
If Buck’s 
was about who Meg Wylie was - she was one of the Talosians with the really large craniums (and bring snickers to little kids who see them from the back). Her character has the lion share of the speaking roles, though I’m not sure if her voice is used.
If the ??? was about Michael Rennie (who I regret to inform you died in 1971), he played Klaatu in The Day the Earth Stood Still - and that Lost In Space is also a classic.
I think in the original “Cage,” Malachi Throne supplied the voice for “The Keeper.” When it was re-edited into “The Menagerie,” though, they dubbed someone else’s.
Thanks for the clarification, Corbomite.
Meg also had a recurring role on Mad About You, as an aunt of indeterminate relation.