You know when you showed up, I was like, 'Yeah right, like I'm gonna let that scrub on my ship.' But it was a slow day, no big planets to dominate, nothing but re-runs on, so I figured, 'Maybe he does have some secret super-weapon. At least it would be... entertaining.' But you know what? I never guessed what a pathetic waste of time you'd be. Do you really think I would let you ride my coat-tails to the top? Ha! GET REAL, BUSTER!! NOT EVEN THAT IDIOT HATER IS AS DELUSIONAL AS YOU!!
~ Lord Dominator showing her superiority to Emperor Awesome and Lord Hater in disguise.

In works of fictions starring many villains, there can be either a main antagonist for each story arc or a Big Bad standing at the top of the hierarchy. In the latter case, however, one (or sometimes more than one) villain even more powerful and influential than the Big Bad himself can be introduced: the aptly-named Bigger Bad, also known as a Greater Scope Villain. Exceptions aside, the Bigger Bad ultimately has a smaller role than the Big Bad in focus.

However, the Bigger Bad is pretty much the main reason for the circumstances in the story that usually wouldn't be (naturally) possible to occur (pollution, artifact of doom, evil ancient group to which the Big Bad used to belong/is acting as a leader, etc). They can also be the main supply of power for the Big Bad, and sometimes the very motivation for said Big Bad to act villainously. Should the story ultimately end up putting more focus on the Bigger Bad, it may over-cede the current antagonist as the Big Bad. This type of villain often serves as an unseen character or is revealed at the very end of the story.

HIGHLY IMPORTANT: A Bigger Bad can logically ONLY appear in stories with a Big Bad. A Big Bad CANNOT be a Bigger Bad at the same time, unless there is a spin-off series in which one of his servants serves as the Big Bad.