From the Super Mario Wiki
Bowser holding the Star Rod
The Star Rod is a magical rod that can make wishes come true. According to Russ T., ancient magic created the Star Rod long ago. Bowser steals the Star Rod from Star Haven at the beginning of Paper Mario. He uses it to grant all his evil wishes. Activating it, he easily defeats Mario by making himself invincible. Mario and his partners must save the seven Star Spirits to deactivate the Star Rod's power.
In the final two battles against Bowser, the Koopa King is aided by Kammy Koopa who uses a machine to increase Bowser's strength dramatically on top of the the strength the Star Rod had already given him.
Names in Other Languages
Sutā no Tsue