Caim is the main protagonist of Drakengard, however he is widely considered a Nominal Hero, which is basically what is known as "Hero in name only": in other words if Caim was not fighting an enemy far more brutal than himself he would be considered an outright Protagonist Villain.
In Drakengard 2, he becomes the antagonist, pursuing Nowe and his party. Nowe fought him and he won the battle. Later on, Caim contacts him into ending Angelus' suffering by killing her. Doing so is not only the end of her life, but also Caim's. He dies smiling at Nowe, thanking him for doing his duty.
Caim is a soldier of the Union and was originally the next in line for becoming King of Caerleon before his parents were murdered by a dragon, now motivated primarily by his love for his sister Furiae and a need for revenge. After suffering a grievous wound in battle, he stumbled across a similarly wounded red dragon called Angelus, and forged a pact in order to preserve both their lives. The superhuman abilities and new flying mount were a pleasant bonus, though at the cost of his ability to speak. Together with Angelus and his other, even more flawed, travelling companions, they set out to the defeat The Empire.