Karn

Planeswalker Urza created the golem Karn as a weapon and artifact. A Planeswalker himself, Karn has built—and is now trying to save—the metal world of Argentum, which has been contaminated and corrupted.

A brief history on this Planeswalker
The Planeswalker Urza created Karn as a war weapon. But he’s had many other purposes to serve. Able to control all five colors of mana, this silver golem is a time-travelling Planeswalker, powerful artifact, world builder, and unstoppable ally.

Karn was the first artifact of the Legacy, a collection of objects whose arcane might could be used against Phyrexia, an artificial, all-mechanical plane. Decades later, when Phyrexia invaded the plane of Dominaria, Karn fulfilled his destiny, joining with the other artifacts of the Legacy to destroy Phyrexia's Father of Machines. At that moment, Karn became a Planeswalker, inheriting the spark from his creator.

Karn then created a plane of his own: a metal world called Argentum. While Karn was off exploring the universe, a contagion took hold, reshaping the plane and corrupting the mind of the Warden that Karn created to watch over it.

During Dominaria's temporal crisis, Karn allied with Jhoira and the Planeswalkers Teferi and Venser to prevent time itself from collapsing. In the process, he became susceptible to the contagion on his created planet. His mind addled and broken by the corruption, Karn escaped to Mirrodin, where we was hailed as the next Father of Machines by the new Phyrexians.

The Planeswalker Koth sought allies to help save Mirrodin, his native world. He recruited Elspeth Tirel as well as Karn's friend Venser. When the trio arrived, they found the plane poisoned beyond saving. To help prevent the corruption from spread to other worlds, Venser sacrificed himself, giving Karn his immunity to the contagion.

Grief-stricken by the fate of Argentum and the death of his friend, Karn travels the universe, retracing his steps to find the contagion’s source and finally defeat it.

Recent Activity
Not much is known of his travels after New Phyrexia conquered his created planet. It is known that the planeswalker is alive.