It was originally a prototype cosmic rod made by Ted Knight, the Golden Age Starman. He retired after the events of Zero Hour and passed the mantle to his son David.
David was Starman for a hot minute before he was killed by a sniper in a crime wave started by the children of The Mist, one of Ted's oldest foes. David's hipster brother Jack, who never wanted to be a superhero, reluctantly takes up the cosmic rod (but not the tights) and avenges his brother.
After a few years of being Starman, Jack decides to retire and he passes the rod to Courtney, who goes from being the Star-spangled Kid to Stargirl.