The Star Rod is an item in Paper Mario. It is a magic rod that makes wishes come true. It was made long ago by ancient magic, according to Russ T., a Toad in Toad Town. However, it is stolen from Star Haven by Bowser at the beginning of the game. When Mario tried to take it away from him at the beginning of the game in Princess Peach's Castle, he was defeated easily, and he was knocked out of a window because Bowser had made himself invincible. To defeat Bowser, Mario must take all seven Star Spirits back to Star Haven.
In battle, Bowser uses the rod to perform attacks in addition to physical attacks. The Star Beam (later becomes Peach Beam) can rid Bowser of his invincibility until he uses the rod again.