Ravager is an autobot. He was formerly a Decepticon but during the destruction of Cybertron he decided to help Optimus Prime. At Cybertron's destruction he was presumed dead, but secretly was alive, having flown to Earth shortly after Megatron.
Destruction of Cybertron
When Megatron gathered up his decepticon seperatists Ravager was one of the first to join his ranks. He became Megatron's third in command (behind Starscream). During the fateful day on which Megatron destroyed Cybertron, he was enraged by Megatron's actions and killed lots of decepticon drones.