Jack isn't even the hero of the episode, the Lava Monster is. He shows up like a badass, and you think he's the villain due to the setup, but you learn he's just like Jack, a warrior that fought against Aku, but ultimately failed. Aku, being the ass he is, punished him by making him live forever, trapped in the heart of a mountain. For thousands of years he was in sensory deprivation and solitary confinement (which IRL will drive someone insane in a matter of days for most), but his will was strong, and he retained his identity, eventually overcame Aku's imprisonment, and even turned the material of his prison into his own new body, to give himself freedom to move again. But since he's a Viking, he just wants to be with his people, who are all dead now. But, again, Viking, so the only way he can go to heaven, is to die in combat. So he makes a death trap, and lures warriors to fight him, hoping beyond hope that eventually, one strong enough to kill him (in his new badass form) will show up, and defeat him. The story is told so fucking well by the voice actor, you can FEEL his sadness and misery, and loss of all but hope. And when Jack, after hearing the story, stands up, draws his sword, and says "Prepare yourself", the reaction of the Lava Monster is perfect. His voice, a mixture of relief and anticipation. "AT LAST! THE GATES OF VALHALLA....OPEN TO ME!!" And then they clash, to an awesome drum sequence. Fast paced, frenetic, intense. The Viking gets a strong hit against Jack, and knocks him down. He cries out "RISE WARRIOR, RISE!! Honorably I must be defeated, I CANNOT let up!" So you know he's not throwing the fight. But he WANTS to lose, it's all he wants in the world, but he can't give the victory easily, or else he won't get into Valhalla. They fight again, and finally Jack lands the killing blow (and I don't care what anyone says, he killed a human being in this episode. They try to cover it with him dying of old age, but he has to die in battle, which means that Jack killed him, otherwise he wouldn't get into Valhalla. But his reaction when he is dealt the mortal blow. As his body begins to change, releasing the magic Aku used to imprison him, he yells out, defiant and victorious. "ACCURSED MONSTER!! YOUR SPELL IS BROKEN!!" He is freed of Aku's magic, restored to his human form, and then dies. As Jack kneels over him, saddened at the loss of the man, light shines down from above (they are miles under the earth), and two Valkyries ride down on the beams of light, and claim his body, taking him to his rightful resting place in Valhalla. The episode ends with Jack leaving the no longer tainted lands, and panning up to see the warrior in Valhalla, at last free and happy.