Yawgmoth is based on The Lord of the Wastes in Dominarian mythology, thethe medical genius of the Thran Empire who was banished for his highly controversial solutions to medical ailments. Yawgmoth was not given a form in the card game.
Upon discovering the artificial plane of Phyrexia, Yawgmoth felt an increasing desire to utilize this mechanical plane to his own ends. He became the god of that plane, but his true dream was to return to his home plane of Dominaria and turn its inhabitants into "perfect beings" under his rule. The main antagonist throughout multiple MTG sagas, he is one of the most well-known villains in the MTG multiverse.