Some nominations:

Muhammad Ali - The Greatest
Walter Payton - Sweetness
Karl Malone - The Mailman
Randy Johnson - Big Unit
Ken Griffey Jr - The Kid
William Perry - Refrigerator
David Ortiz - Big Papi
Roger Clemens - The Rocket
Bill Parcells - Tuna
Erving Johnson - Magic
Deion Sanders - Primetime
Wayne Gretsky - The Great One
Roberto Clemente - The Great One
OJ Simpson - Juice
Christian Okoye - The Nigerian Nightmare
Babe Ruth - The Great Bambino, The Sultan of Swat, The Caliph of Clout, The King of Swing, The Behemoth of Bust, Jack Dunn's Baby, The Big Bam, The Big Fellow, Jedge, The Wazir of Wham, The Maharajah of Mash, The Rajah of Rap, The Blunderbuss, The Mammoth of Maul, The Mauling Mastodon, The Mauling Monarch, The Wali of Wallop, The King of Crash, The Prince of Powders, The Terrible Titan, The Kid of Krash