"The Senate" would be a correct answer, for one, continually undermining the democratic aspects of the Republic for their own oligarchic power. "Augustus" I would also regard as more correct than "Julius Caesar".

The technical answer is Octavian/Augustus the first Emperor of the Roman Empire

Why not "the optimates?" The answer doesn't necessarily need to be one person.

The patricii would be a good quick answer.

That said, Caesar killed it like a lion kills a very sick gazelle. Without the lion the gazelle probably still dies, but may recover.