He was a badass for sure; a capable commander and fighter. I won't dispute that. But IMO his hype is solely based on him slaying Prince Rhaegar on the Trident (his other notable victories in combat are against Randall Grafton and Lord Fell). Rhaegar was a capable fighter as well but he wasn't exceptionally great. Brandon Stark could very well have been the one to kill him and win all the notoriety. As for his victories as a commander, Robert had a few notable wins. He won three battles in