A fat, bald thief with an egg-shaped body who rides on a rocket powered hobby horse and specializes in stealing collectibles. After escaping from Superboy during their first encounter, he starts to send the Boy of Steel clues to his crimes in order to taunt him until Superboy captures him (SB No. 6/1, Jan/Feb 1950: "The Hobby Robber!"). His real name is Robert Hobb.
Humpty Dumpty later escapes from prison and begins stealing dolls. As before, he leaves clues for Superboy that ultimately allow the Boy of Steel to capture him (SB No. 7/2, Mar/Apr 1950: "Dolls of Danger!").
Humpty Dumpty escapes a third time and this time begins stealing flags with the assistance of two armed thugs. They force Superboy to promise not to contact the police in any way, not even with signal flags, by threatening to shoot a hostage in the head. Superboy tricks Humpty Dumpty into believing that he's gone back on his word by hoisting a hospitality flag which causes nearby ships to start sailing for Humpty Dumpty's ship; Humpty Dumpty mistakenly believes that these ships are law enforcement vessels and flees. He is soon captured by Superboy and returned to prison (SB No. 8/2, May/Jun 1950: "The Flags of Crime!").
Humpty Dumpty escapes yet again and steals model boats before being recaptured by Superboy (SB No. 9/3, Jul/Aug 1950: "Ship Ahoy, Superboy!").
Upon his next escape Humpty Dumpty begins stealing "famous firsts." As usual he is captured and returned to prison by Superboy (SB No. 11/3, Nov/Dec 1950: "The Famous First Crimes!").
Humpty Dumpty is not seen for many years before he finally returns to face Superboy again, this time as the Curator. During this incident, while using Red Kryptonite, he causes Superboy to temporarily lose his sight (NSB No. 24/1, Dec 1981: "Blind Boy's Bluff").