At first glance, Astrotrain appears to be a colossal Triple Changer amongst the Decepticons, using his force fields, dimensional portals, and vehicular mode manipulation for both his own selfish gain and to occasionally fuel his sadistic streak... if it's Dead End.
All subsequent glances will reveal that this is in fact an excellent summary of Astrotrain, save for one detail that lets Megatron control him: he is absolutely terrified of his former master. And he will do anything, whether that includes shooting down helpless Autobots or working with Dead End, to avoid the tyrant.