I think Agoston is the best candidate to tame the savage Spirit of this dragon. Let's count down the pros here. He's already got fire powers, so the upgrade is on brand. He's a physical attacker, and spirit would likely make him beefier. He wight get wings to carry him into battle more swiftly. Finally, The dragon won't be able to drive him to rule the world, because that would mean he would be betraying the emperor. I think its a good fit, if no one else wants to enthusiastically call dibs.