Aro is one-third of the Volturi, the oldest and most powerful vampire family. As the closest thing in the vampire world to a royal family, the Volturi act as the governing body over all vampires. Aro, along with his companions, Marcus and Caius, live in a castle fortress in Volterra, Italy. Their likeness was depicted by the painter Solimena - the painting still hangs in Carlisle's study.
When Carlisle came to live with them for a while, Aro tried to cure him of his "aversion to his natural food source", but failed. The two still remain friends to this day.
With his extraordinary talent to read every thought a person has ever had simply by touching them, Aro is certainly a formidable force, but this is tempered by his genial personality. He acts as a jovial and enthusiastic spokesperson for the Volturi when Edward, Alice, and Bella are in Volterra. He has a great regard for talent, and he refused to aid in Edward's suicide attempt mainly because he was interested in his mind reading abilities. His great curiosity in seeing what talents Bella would have as a vampire also played a huge role in his consent to let them go unscathed.
Classic Quotes-
"Ah, Jane. You are such a comfort to me." (New Moon, pg. 467)
"You see, Edward? What did I tell you? Aren't you glad that I didn't give you what you wanted yesterday?" (New Moon, pg. 468)
"Marcus, Caius, look! Bella is alive after all, and Alice is here with her! Isn't that wonderful?" (New Moon, pg. 469)
"Ah, how I miss my friend Carlisle! You remind me of him-- only he was not so angry." (To Edward, New Moon, pg. 471)
"But your restraint! I did not know such strength was possible. To insure yourself against such a siren call,
not just once but again and again-- if I had not felt it myself, I would not have believed." (New Moon, pg. 472)
"Caius, surely you see the potential. I haven't seen a prospective talent so promising since we found Jane and Alec. Can you imagine the possibilities when she is one of us?" (New Moon, pg. 477)
“In truth, young Bella, immortality does become you most extraordinarily. It is as if you were designed for this life.” (Breaking Dawn, pg. 696)