4. Brainiac
There are many incarnations of Brainiac as a character but
it's core characteristics remain intact. Brainiac's main purpose is to gain absolute knowledge and to destroy and conquer all life. As an android, Brainiac has no moral compass and is considered to be an android of a '12th level of intelligence' making him absurdly brilliant and all the more dangerous. Brainiac wont rest until he acquires infinite knowledge and conquers all worlds. That's where Superman gets involved.
How would you introduce him in the movie? In his continuous quest for infinite knowledge and domination, Brainiac stumbles upon a little planet called Earth. Thinking nothing of it, Brainiac goes about absorbing all of Earth's technological knowledge until he's eventually met by Earths savior, Kal-El. Brainiac's quickly defeated but not beaten. Gaining a better understanding of who the man from Krypton really is, he eventually reappears after upgrading and improving himself. Making him The Man of Steel's most worthy adversary to date. Just thinking of all the advanced technology that could be used for a movie of this caliber is mind blowing. It'd be pretty badass to see.