Thoros was born in the Free City of Myr. Being an eighth son, Thoros' father had no means to support him and gave him up to the local Temple of the Lord of Light. There, he was raised to become a Red Priest, though he grew up a gluttonous and lustful man, constantly raiding the kitchens and taking girls to his chambers. He fought for King Robert Baratheon in the Greyjoy Rebellion. He was the first man, followed closely by Ser Jorah Mormont, through the breach during the Siege of Pyke, stabbing and terrifying the ironborn with his flaming sword.