This is really hard.
2. Andre the Giant
3. Stone Cold
4. The Rock
Flair, Undertaker, Ultimate Warrior are tough omissions.
I know almost nothing about wrestling, but this would be my list, as well. People keep talking about Rick Flair like he is a lock and I have barely heard of the guy.
I realize my lack of knowledge greatly limits my credibility, but as far as popularity and covering more than one generation (the 80s) goes, this seems like a good list.
I think that your lack of familiarity with Flair may be because the WWF/WWE has been better at marketing than any other wrestling company. It's not a coincidence that Hogan was in Rocky III, or that Andre was in Princess Bride. I put Vince McMahon on my list, because the guy is one of the great marketing geniuses of any business, ever.
But, for those who follow wrestling, Flair is truly legendary. 40 years, a kazillion titles, an iconic look (the robe), nickname (Nature Boy) and catch phrase ("Wooooooooo!").