Superboy is a clone grafted with Superman's DNA (as opposed to a younger version of Superman), who was introduced in 1993. He was created by Project Cadmus to replace Superman following the Death of Superman story, and was artificially aged to mid-teens and implanted with the necessary knowledge of someone his biological age (in regards to general studies, such as math, reading, etc). Before the experiment could be completed (i.e. aging him to full adulthood and implanting him with safeguards to control him), he was freed by the Newsboy Legion and escaped. One of the boys gave him a leather jacket before he set out into the city (having his first brush with being Superman when he encounters Sidearm attempting to rip off an ATM).
More on this character soon, for the mean time read his bio here: