What was the name of transformer who switch sides and a prime in movie transformers revenge fallen?

The Transformer who switched sides and was also a Prime in Transformers: Revenge of the Fallen is The Fallen.

He was originally a Prime alongside Optimus Prime, but he believed that the only way to save Cybertron was to harvest the energy of the Sun and became a ruthless tyrant. He was resurrected by Megatron and convinced the Decepticons to help him achieve his goals.