Starscream

Starscream is a Decepticon who often betrays Megatron in order to become ruler of the Decepticons himself, but he rarely comes close to doing this.

Transformers
When Megatron is released from his icy prison, he is informed by Starscream the humans have the All Spark, much to Megatron's frustration, who says that Starscream failed him again. Starscream puts Bumblebee, Ratchet, and Ironhide out of the battle by firing missiles at them, which destroys Bumblebee's legs. He destroys a helicopter that was supposed to transport Sam. When F-22 fighter jets fly into battle, he transforms into one and conceals himself amongst them before transforming in mid-air and destroying three jets when the F-22 jets shoot at him and he flies away back into space

Revenge of the Fallen
Megatron is brought back to life after being killed before, and he flies back to The Fallen's ship, where he is confronted by Starscream. Megatron scolds Starscream for leaving him, and Starscream tries to justify this by saying he did it to rebuild the Decepticon army and that with Megatron gone someone had to take over. This heavily implies that the real reason he left was so Megatron would die and he could take his place. This doesn't work and Megatron knees Starscream in the face and slams him into the wall, saying that even in death their is no command but his.

Starscream partakes in the fight against Optimus, and shoots him several times. Optimus retaliates by ripping off Starscream's arm and hitting him with it. After Optimus dies, Starscream and Megatron flee. Megatron attacks Starscream when he reveals he didn't capture Sam, who protests and say Sam is one in 7 billion. He is then shown re-attaching his arm. During the final battle and The Fallen is killed, Starscream tells Megatron that sometimes cowards do survive before he and Megatron fly away.

Dark of the Moon
Starscream, along with Megatron, Soundwave, and Igor are hiding in Africa. Starscream pretends to be simpathetic to Megatron's face injury that was inflicted on him by Optimus in the previous movie. Megatron calls him a gaseous sychophant, apparently knowing Starscream was pretending. When the Decepticons invade Washington D.C., where they kill nearly everyone in Chicago. Starscream compliments Megatron's decision to side with Sentinel Prime. When the Autobots supposably leave in the Xantium, Starscream shoots it down in case the Autobots return. However the Autobots were hiding in a container unduer the Xantium. During the resulting battle, Starscream confronts Sam and tries to kill him. However, Sam impales Starscream's eye with his grappling hook and stabs him in the other eye with a boom stick. Sam is rescued by Bumblebee as Starscream explodes.