Originally Posted by Darth54
The wookiepedia bit is quite interesting.
But I believe that the OP wanted to know how *Sidious*, not Lucas, found the name. It's been a while since I read the book, but there's something about "Sith spirits" whispering the name to Sidious. Or something similar.
Yep, in fact, if you pay attention in the movie, Sidious doesn't just say "You'llbeDarthVader." He kind of says "You'll be Darth... Va... Der." In the space between syllables you can hear a really creepy sound, probably the Sith spirits telling him the name.