Frostwraith
The Demon King
I choose the number 4.
Popularity is not everything, indeed, but retro characters are always neat additions to the roster and gives spotlight and may even revive their series, like what happened with Pit.I'm using KOS-MOS as one of those really random choices. I agree with you that not everyone gets in based on popularity.
I kind of address G&W, R.O.B, and retros with the whole Wayne Gretzky thing. Maybe they aren't legendary, but they are being revived as something to remember from history.