He is a sort of bellwether of bad guys to come in Season 4.
He is not human, and we want to start playing with the idea that Earth hasn’t always belonged just to our kind.
Not to get deep into immigration metaphors, but Mallus is an ancient evil, he doesn’t understand humans and doesn’t understand why we have any claim to controlling this world of ours.
It’s kind of presumptuous for anybody to think they have ownership of this Earth or any part of it.