I think he is a big bully. His only motivation is intimidation. He thinks that just because he's part of the Volturi that he is indestructible. Which I don't believe is true.
I think without Aros being around, Caisus would totally wipe out any vampire coven that had some sort of "normal" life and lived with humans better then them.
I also think that he is so very much intimidated by Carlisle and afraid of him and if Carlisle wanted to, he could bring down the whole Volturi.








