I think he is the type to know to position himself with the most popular, or the most powerful to gain favor, or power. I think he molds himself to be whoever he's friends with that day.
He's not dumb by any means, I don't think. He's a Slytherin, which shows that he's cunning and sharp.
I also think that he learned his manipulative-ness from his mother, who had seven husbands that mysteriously died, leaving her wealth. She learned to use her beauty to her benefit.
What other effects do you think his mother has had on him?
Well, what do you think? What's his story?