Glacian

Glacian was an ancient Thran artificer who designed many of the Thran Empire's most powerful artifacts, including the powerstones on which Thran technology was based.

History
After being stabbed with a powerstone by Gix, one of the Untouchables, Glacian caught the disease phthisis, which was caused by long exposure to powerstone radiation. When Thran healing magic only made the disease worse, his wife, Rebbec, used her influence in the council to recall the healer Yawgmoth from his exile.

Yawgmoth discovered the cause of phthisis and even created a serum that stopped the disease; but, for some reason, it had no effect on Glacian. His disease only progressed, with him developing multiple personality disorder. Glacian became increasingly paranoid and began to think of others as traitors, as Yawgmoth had become one of the most powerful people in the empire.

Yawgmoth had fallen in love with Rebbec and was trying to marginalize Glacian, banishing him to the Caves of the Damned. Trying to look good for Rebbec, Yawgmoth did remove the sliver of the powerstone that had been keeping Glacian ill from his old wound, but replaced it with the two halves of the powerstone Dyfed had used to create a permanent portal between Dominaria and Phyrexia when Rebbec wasn't looking. The radiation of these stones killed him, but his essence was trapped inside them. Finally being able to think clearly again, he convinced Rebbec to unify the halves and use them to close the portal to Phyrexia forever.

Glacian possessed the planeswalker's spark, but it was never triggered.

Note
The powerstone used by Yawgmoth is the same stone that was found years later by Urza, Mishra, and their teacher Tocasia. The stone split again when touched by the brothers. The resulting explosion left each brother holding half of the stone. One, the Mightstone, made creatures stronger and the other, the Weakstone, made them weaker. Each brother's desire to have the other half led to the "Brothers' War".