From A Wiki of Ice and Fire
Master-at-arms of the Red Keep
|Died||In 299 AC, at King's Landing|
|Book(s)|| A Game of Thrones (Appears)|
A Clash of Kings (Appears)
A Feast for Crows (Mentioned)
A Game of Thrones
When Lady Catelyn Stark and Ser Rodrik Cassel go to King's Landing in search of the owner of the dagger used by the man who attempted to kill Bran, Rodrik visits Ser Aron, who as master-at-arms might recognize it.
A Clash of Kings
He was part of the escort that was attacked by the citizens of King's Landing after attending Princess Myrcella Baratheon's departure for Dorne. He was slain by the angry mob and his dead body was found unrecognizable near a stone that was used to smash his skull.
A Feast for Crows
Aron Santagar has not been replaced yet. It is revealed that he was Dornish.