The Almighty Tallest
The Almighty Tallest is an honorary and physical title given to the entity (or entities, if there's a tie) who are chosen by the control brains to run the Irken Empire. There are currently two leaders, Almighty Tallest Red and Almighty Tallest Purple. Red seems to be a bit more intelligent overall but the pair rule well in concert - rarely if ever disagreeing on the course of action which should be taken.
The previous Almighty Tallest was Miyuki who was killed when an infinite enerty absorbing beast designed by Zim escaped and ate an infinite energy generation machine - the beast rapidly grew out of control and ate Miyuki before disappearing into space.