As someone already said, Ronaldo was engineered. A mad scientist used all the best techniques of today and created a "perfect" footballer. Messi is more natural. He's the protagonist. Like Goku. He can constantly grow because of his immeasurable talent.
In planet Earth terms, Messi is the all-encompassing Mother Nature while Ronaldo is all the machinery of the world.
He also plays for an engineered team, Real Madrid, which often likes to just buy up all the talent and force their way to the top. Remember the Schuster era when they couldn't win shit even though they had Beckham, Figo, Zidane and all those superstars? Yeah, compare that to the naturally-grown Barcelona with players from La Masia like Xavi, Iniesta, Messi.
Anyway, let's not turn this into a Barca vs Real thread.
Ronaldo is a great player. But no matter how many times he hires the engineers to give him more pretty bells and whistles, his rival on the other side is a walking miracle. He can never be Number 1. And that's probably why he acts like a douche on the field.