Lex Luthor, who is portrayed by Michael Rosenbaum, was a series regular on Smallville from the first season until the seventh.  Lex, of course, grows up to be Superman's infamous arch-nemesis.

Lex Luthor Quotes

A man is judged by the quality of his friends. If the quarterback's with them, he'll have to face the consequences.

Lex

Lex: Clark...do you believe a man can fly?
Clark: Sure. In a plane.
Lex: No, I'm not talking about that. I'm talking about soaring through the clouds, with nothing but air beneath you.
Clark: People can't fly, Lex.
Lex: I did. After the accident, when my heart stopped. It was the most exhilarating two minutes of my life. I flew over Smallville, and for the first time, I didn't see a dead end. I saw a new beginning. Thanks to you, I have a second chance. We have a future, Clark, and I don't want anything to stand in the way of our friendship.

Smallville Quotes

I'm about as real as it gets.

Chloe

Oliver: You've done a hell of a job keeping the world safe on your own, Clark. I'm here to help you now.
Clark: Good. Something tells me...soon the world will need all the help we can get.