1. NATURE BOY Buddy Rogers (and his clone - Ric Flair)
2. STONE COLD Steve Austin
3. CEREBRAL ASSASSIN Triple H
4. RABID WOLVERINE Chris Benoit
5. DEADMAN Undertaker
I don't know if it's true, but I understand that Steve Austin's first wife came up with the nickname "Stone Cold" by accident. She was British and one day she became distracted and left her cup of tea on the table. When she returned to drink it she remarked, "This tea is stone cold!" I don't know if this is really how Austin came up with the nickname, but it's a good story nonetheless.
A fan supposedly came up with "Nature Boy." Buddy Rogers was wrestling either in Texas or California and was looking especially tanned and buff for one show. As he made his way to the ring a fan yelled out, "Get a load of the "nature boy!" The name stuck and "Nature Boy" Buddy Rogers went on to make wrestling history.