Krark

Krark was a legendary goblin wizard on Mirrodin who traveled to the hollow center of the plane and cataloged his journeys in a book. The Krark-Clan is named after him.

History
Krark was a high-rolling gambler who lived in the Oxidda mountains of Mirrodin. He lost both his thumbs to Durg betting on a hellion race, including his luckiest thumb. Krark wanted that thumb back. He bet Durg a thumb that he could walk to the center of Mirrodin and back. Durg pointed out that Krark didn't have any thumbs left, but Krark said that he was good for it. Krark traveled deep within the center of Mirrodin. Weeks later, he returned bearing a book he'd written, filled with a description of his journey. Durg sighed and handed over Krark's Thumb. Krark wore the thumb around his neck along with his other good luck charms until the end of his days (which wasn't very long, as his journey got him executed for heresy).

Cult of Krark
After he died, a religion known as the Cult of Krark was formed around his writings, spreading the word that there was a secret world inside of Mirrodin. The religion holds that Mirrodin is hollow, and its leader preaches from the Book of Krark. The Book of Krark states that if you look at the mana core, your eyes will turn to ashes and your feet will turn into goat hooves. Krark is believed by his cult to guide the souls of the dead to the Steel Mother.