Where the bad Transformers that defected to the good side?

I feel like a total nerd asking this. But wasn't one of the autobots originally bad? I can't remember....Where the bad Transformers that defected to the good side?In the original cartoon Jetfire was friends with Starscream so when he was discovered he joined his side, but he didn't agree with their ways. He joined the Autobots after the whole affair because he believed in their cause