The origin of Booster Gold is presented in "To Cross the Rubicon."
Jason Redfern while going for a bike ride in Metropolis's Centennial Park he finds what he thinks is a toy spaceship. He soon finds out that the ship and pilot are real. The pilot is only about five inches tall, and Jason doesn't understand his language so he calls him Z. Jason does not know Z is Ranzee. Jason takes Ranzee home were Ranzee is able to expel energy that looks like Superman's 'S' shield. Of course Jason has no way of getting a hold of Superman so he goes to Goldstar Inc. in an attempt to get a hold of Booster Gold.
Jason is able to convince Trixie Collins a.k.a Goldstar the receptionist/secretary for Booster's company to let him see Booster. He is able to do this by showing her Ranzee. Booster sees Jason as soon as possible. When Jason explains his story he shows Ranzee to Booster. Ranzee expels energy again showing booster the same thing he had shown Jason. Booster gets the message out using the Metropolis media. Telling Superman to meet him at Baker Dam.
Superman is ticked at Booster and demands to know who he is Skeets tells Superman Booster's shady origin. This upsets Booster and he gets into an argument with Superman. This ends quickly when everyone is zapped and completely knocked out by a new alien who in unknown to everyone. This Alien will be relieved as Lord Galeb.