What exactly drove the original warrior to shove the soul stone into his own head? Decard Cain said that it was arrogance, but was that it? Did he have pure intentions when he did that? Did he want to be like the Mage who was holding Mephisto? Or did he want Diablo's power for him self?
I always thought that after seeing the Prince die on the ground the warrior decided to contain the power of Diablo within himself so nobody else would have to suffer that fate.