Fan Casting The Starscream in Sort by Tropes

A certain type of character falls outside the pattern: a villain too ambitious or individualistic or just too stubborn to accept the supremacy of the Big Bad. Instead, this villain actually dreams about overthrowing the guy everyone else fears and taking his place. Sometimes he is a (grudging) servant of the Big Bad; sometimes he is entirely outside the established power structure. In rare Noble Demon or Anti-Villain cases, he may be actually loyal to the Greater-Scope Villain, and feels his direct boss isn't. In any case, if the Big Bad ever stumbles or shows weakness, the Starscream will be there, ready to kick him out of the Astrotrain.