Zagi and Gary Smith, both of them are same personality. Indeed, there's has notably difference:
1. Zagi are actually possessing from previous professor, while Gary Smith was just regular people.
2. Zagi did killed they parents, while Gary Smith doesn't.
3. Both of them are manipulate people, but the difference is Zagi manipulate each character in each arc. While Gary Smith Manipulate all cliques.
4. Because of this, both of them are same objective; taking everything he wants. The difference is Gary Smith was only taking one city, while Zagi, taking over the world.
5. Gary Smith doesn't had people that gotten PTSD to anyone who picked on them, while Zagi did want people get PTSD to anyone by eaten or beating to death.
6. Gary Smith doesn't summon like monsters, but only that if the students wants Jimmy to get beating up, while Zagi did summon monster more often to making destruction.
That's similarity for my reason.