Ian McDiarmid (born 11 August 1944) is a Scottish actor and director best known for portraying Emperor Palpatine in the Star Wars film series. He has received an Olivier Award for Best Actor and a Tony Award for Best Featured Actor in a Play for his performances. Wikipedia
After defeating Sinestro and dealing with the treason of another friend, Hal Jordan has to fight Mongul, the son of the conqueror that once tried to invade Earth.
