Starscream is Megatron's right-hand man, and Decepticon commander in his absence, whose ambitions are to seize control of the Decepticons and overthrow Megatron to defeat the Autobots by any means necessary. But though he talks a big game, he is a coward at heart, and when his schemes ultimately fail, he resorts to whimpering, cowering, and pleading for mercy from Megatron to ensure that he didn't get rid of him for long. He leads a small splinter faction of Decepticons called the Seekers, with two of them, Thundercracker and Skywarp, as his personal wingmen and enforcers.

Starscream's voice needs to balance the feeling of ambitious backstabbing underling and hapless cowering shmuck, yet still be a threat to the Autobots. You may refer to Steve Blum's performance in TFP for inspiration, but you may also look into the live action movies and other performances of this famous character, including the late Chris Latta's G1 performance.