You and starscream both worked for Megatron. When Megatron destroyed the auto bot's planet whilst looking for the all spark,you joined him,starscream joined later on. You were one of the most powerful warriors in Megatron's team so losing you is like losing your child in the supermarket and never finding them ever and your so heartbroken that you kill yourself,which is why Megatron was reluctant to send you but eventually gave in. You found that Optimus prime and the surviving autobots were taking refuge on earth were the all spark was also located. You and starscream went down to earth to get to the all spark before Optimus prime did. Unfortunately the All spark was in the hands of a human named Sam witwicky who they already have a hold of,you managed to track they're location to a workshop

You and starscream arrived with a dramatic entrance of course.

optimus:"Everyone! Fall back,I will handle them"

Bumblebee:speaking through his radio "are you sure you can handle them?"