Universe Boy is an amalgam of Ultra Boy and Captain Universe. There are two very distinct versions of him, one of which only came into existence due to the collapse and reforging of reality. 
 
The somewhat cocky and arrogant "Pre-Crisis" version, who looked more like Captain Universe than he did Ultra Boy, accidentally told Spider-Boy that he was going to die in his fight with Scavulture (an amalgam of Scavenger and The Vulture).
 

He then participated in the battle against The Frightful Five (an amalgam of The Fatal Five and The Frightful Four teams) shortly before time and space collapsed.
 
When he was rebooted into the "Post-Crisis" Universe Boy, his appearance had altered, making him look more like Ultra Boy than Captain Universe. 
 
Unlike his "Pre-Crisis" self, this Universe Boy was, on the surface, more respectful and obedient but never uttered a word and remained in the background looking at Spider-Boy, who was an idol to both versions of The Legion of Galactic Guardians 2099, in awe for the duration of the time Spider-Boy spent in their future.