As his father grew older, Carlisle assumed his role.
One night, he was attacked by a vampire and left to die on the streets.
Carlisle has had centuries to perfect his medicinal talents, therefore making him an excellent doctor.
Unlike most vampires, he is not at all tempted by the scent of human blood, due to the over 300 years he has spent holding back his temptations.
He falls in love with Bella soon after she arrives in Forks.