It's a little weird how Crystar went from a short lived fantasy themed toy line to Danzig. Though that story has been told countless times on the internet, I'm here for the Crystal Warrior himself. Crystar was a creation of Marvel comics realized into toys by Remco. I usually make a joke about how most fantasy toy lines are walking heavy metal album covers and use left over Halloween decorations. Aside from the whole Danzig thing, that's a pretty good description of the Crystar story line. And I quote directly from Wikipedia.
Years ago, The Demon Lord sent his demon armies to conquer the world of Crystalium. The King of Crystalium led the fight against the Demon Lord in the Chaos War, but he was killed during the war. The forces of Order then sent the wizard Ogeode and the Prisma-Crystal to drive away The Demon Lord's minions and the forces of Chaos. In his defeat, the Demon Lord made the "Prophecy of Chaos", that he would one day send another of his servants to divide the planet against itself and bring ruin to all.
After the end of the Chaos War, the wizards Ogeode and Zardeth visited two princes, the brothers Crystar and Moltar, who had to decide whether their people would ally with Chaos or Order. Crystar chose Order and its champion Ogeode. As Moltar considered Chaos, their uncle Feldspar tried to convince him that Chaos was evil. Moltar, feeling that his uncle had always favored Crystar, became enraged and fought Crystar, injuring Feldspar in the process. Leaving them for dead, Moltar led his followers to the Fountain of Fire to find the wizard Zardeth and ally with Chaos.
Ogeode saves Crystar's life by merging him with the great Prisma-Crystal, rendering the prince's body into crystalline form. Similarly, at the Fountain of Fire, Zardeth magically transforms Moltar and his followers with the power of lava. Moltar and his Magma Men then attempt to conquer the city of Galax. Crystar and his warriors, feeling that flesh and blood would prove ineffective against the transformed armies of Moltar, selected an elite group to be transformed into crystal form like Crystar: Koth, Stalax, and Kalibar.