He is portrayed by Michael Sheen.
Not much is known about his human life, but after he became a vampire he became obsessed with power and control. He formed the Volturi and only recruited vampires who's powers where of use to him. He killed his sister because she was of little to no use to him.
Meeting Bella Swan
After Edward Cullen believed Bella was dead, he felt guilty at the thought that he caused her death, so he came up with an elaborate plan to end his guilt. On Saint Salvatore day, Edward decides to break the Volturi rule by revealing the existence of vampires to everyone, but was stopped by Bella.
Regardless, Aro has Edward, Bella and Alice dragged to their chamber and he personally meets them. He prepares his minions to kill them but using his power of tactile telepathy, he analyzes Alice's mind and decides they have potential to become members, but they refuse. Aro still says that Bella is a matter to be dealt with and decides she will either become a vampire herself, or be killed.
When Victoria Sutherland, who Bella previously met, begins making a "Newborn vampire" army, Aro decides that such an army will be dangerous to them and the secret of the vampires. It is known that the Newborns are being create for Victoria's personal anger to Bella. The Volturi agree to help fight the new vampires, but Jane, Aro's main enforcer, tells Bella "The Volturi doesn't give second chances".
The Cullens team up with Jacob Black and the other werewolves, who agreed to help because they knew Jacob cared for Bella, but such and alliance was forbidden. So Victoria's army must be destroyed before the Volturi arrive. Victoria and her minions are defeated just before the Volturi shows up, save for a girl named Bree Tanner, who surrendered. Irregardless, Bree is executed anyways.
Bella was still scared the Volturi would find her and Edward before she turns into a vampire. After Bella does become a vampire, Aro revives a letter with the confirmation, but he says things are not over between him and the Cullens saying "They have something I want."
When Edward and Bella's newborn daughter Renesmee is mistaken for an immortal child, Aro seemed pretty eager about killing them once and for all. It turns out, the Cullens are not the only vampires outside of the Volturi's good graces, so Alice and Jasper search for covens to help fight. The Romanian coven is especially exited because the Volturi usurped their rule over vampires long ago.
The news of Edward and Bella's child being immortal enables Aro to plan an attack on the entire Cullen clan in an effort to kill. To do so, he gathers witnesses of his own to join the Volturi guard, which is also, unknown to him, what Carlisle and his family are doing at that very moment. When the Volturi and their witnesses arrive at a snow-covered field, Aro sees that his prediction had come true about the Cullens gathering witnesses. Carlisle tries to tell Aro and the Guard that Renesmee is not an immortal vampire child. But Aro refuses to believe his side of the story. So he calls up Bella and Edward to him with their protection being the werewolf Jacob Black and fellow vampire Emmett. They respond to Aro's request and bring forth Renesmee so he is to meet her.
Feeling satisfied to see the child, he offers her his hand. But Renesmee uses her own hand with her own gift of seeing the memories of the people around her. Aro then realizes that Renesmee is half immortal and half mortal 'conceived and carried' by Bella while she was 'still human'. After this, Alice and Jasper show their faces and stand up to Aro claiming the truth about Renesmee and that the Volturi's biggest law was unbroken. Alice shows Aro a vision of what might happen if he declares to fight the Cullens and their allies.
In the movie version of Breaking Dawn (Part 2), we are shown the vision through a big showdown that was to happen if the Volturi were supposed to attack under Aro's orders. The fight causes heavy casualties including Alec, Santiago, Demetri, Felix (killed off-screen), Jane, Caius, Marcus and Aro.
Final Fate and Battling the Cullens in Alice's Vision
In the film version of Breaking Dawn, we find that the battle was only a vision. Alice shows Aro proof that Renesmee would not be a danger to their world by presenting a hybrid to him. Aro asks of what age for maturity. He says that he reached the age of 7 when he became a full-grown man. Willing to accept defeat, the Volturi flee the battlefield with the intention that they may loose the battle due to the fact that Bella is a shield to the Cullens and their allies. And Aro is the last one to flee stating to himself 'Such a prize' while looking at Bella, Edward and various other vampires while running away in defeat.
- He is an antagonist in New Moon, a behind the scenes antagonist in Breaking Dawn — Part 1 and the main antagonist in Breaking Dawn — Part 2.