Karn

Karn was created as a probe by Urza since his time travel experiments showed that only silver could pass his time portal unharmed. To make this golem fully intelligent, Urza included Xantcha's heartstone as part of his construction, allowing him to develop an evolving personality. He was befriended by young Teferi and Jhoira, students at the Tolarian Academy, though Teferi saw him more as a toy. When Jhoira's life was taken by a Phyrexian sleeper agent, Karn used Urza's time machine to go back and save her; though he succeeded, the time machine had a catastrophic failure, destroying the first academy and leaving Tolaria a shattered temporal landscape.

Karn returned with Urza and Barrin to help rebuild Tolaria, discovering Jhoira and Teferi still alive, though the latter was stuck in a slow-time bubble. Jhoira and Karn worked hard and eventually devised a method to rescue Teferi. By that time, Karn had been sidelined by Urza, as the planeswalker had moved on to different projects. Karn was always present to serve, however, helping in the Mana Rig and on the Skyship Weatherlight's first mission, to Serra's Realm.

Urza decided that the Weatherlight, Karn, and all the other artifacts he had built and collected over the years to further his quest agaisnt Phyrexia -- collectively, the Legacy -- needed a human component to wield them. He set about interfering with Dominarian bloodlines, trying to breed the perfect hero. The culmination of this project, Gerrard Capashen, was put under Karn's care. To keep Karn from overburdening the boy as he developed, Karn's long memories were locked away, leaving him only a few decades of recollection.

The golem rescued young Gerrard from the Phyrexian raids on Benalia, and brought him to his adoptive father Sidar Kondo. When Kondo's Son Vuel turned against his tribe and stole the Legacy, Karn went to retrieve it. During this effort, he was tricked into killing an innocent bystander, and was frozen by the Touchstone. He was later found and freed by Sisay, with the memory of killing the innocent fresh in his mind. Karn took a vow of pacifism, swearing never again to take a life.

During the Weatherlight's time on Rath, Karn was captured by Greven as he refused to fight off his attackers. He was taken to Volrath's Stronghold. There, he was tortured by being put into a room with an endless supply of Moggs, which he was forced to fall onto and crush to death, until being rescued by Gerrard. On his way out of the Stronghold, he encountered the Sliver Queen, which was guarding the captured Legacy. By explaining to the hive-mind that the Legacy was part of him, Karn convinced the Sliver Queen to let him take the artifacts and depart in peace.

Early in the Phyrexian Invasion, Karn realized his vow of pacifism kept him from protecting his friends and his homeworld. Despite his newfound willingness to kill, he spent much of his time in the Weatherlight's engine core, guiding the ship as it improved itself and further integrated the Legacy. Finally, as all hope of victory seemed lost, Karn united with Urza and Gerrard. When Gerrard placed Urza's powerstone eyes, the Mightstone and Weakstone, into Karn, the Legacy released a wave of white mana, destroying the Phyrexians and defeating Yawgmoth. While the two humans were killed, the powerstones turned Karn into the first -- and, so far as is known, only -- artificial planeswalker.

Karn later created Argentum, a plane of mathematical perfection. He sent probes to monitor Dominaria, but one of them was flawed and became the Mirari. After Karona was defeated, Karn took the Mirari to Argentum and turned it into the golem Memnarch, and left to wander the multiverse with Jeska.

Millennia later, Karn returned to Argentum, now turned to Mirrodin by an insane Memnarch. He turned Memnarch back into the Mirari and left it in the care of Glissa Sunseeker, Slobad, and Geth.

Three hundred years after the events of the Phyrexian Invasion, Karn returned to Dominaria at the request of Teferi to aid him in sealing the time rifts tearing the plane apart. While attempting to close the rift over Tolaria, a corruption brought about by his awakened memories began to take hold of his mind. Sensing this, Karn proceeded to blink throughout the Blind Eternities so he would not be followed across the multiverse - protecting any foolish enough to follow him from a monster of his own creation.

Karn's current status and whereabouts are unknown.