Palpatine is the Chancellor of the Galactic Republic. He is secretly Darth Sidious, the leader of the Sith.
In Lego Star Wars (GBA)
Chancellor Palpatine only appears three times in the Gameboy version of Lego Star Wars: Once in the level Separatist Ship, when you have to rescue him from the prisoner's chamber, and twice as a hologram when issuing order 66 to the clone troopers in the levels Kashyyk Clone Attack and Utapau Clone Attack. The second two times, he is in his Sith Robes.
You can not play as Palpatine.