Grungni was born as one of the first three dwarfs alongside Grimnir and Valaya. He was the father of the entire Dwarf race, and was the one who taught them how to use and shape the metal in the earth.
Age of Sigmar
He returned in Age of Sigmar alongside Grimnir, being found chained to a mountain. He was recruited into Sigmar's pantheon of Order, and helped in the creation of the Stormcast. Other than sending a group to recover the Eight Lamentations (a series of deadly weapons), he hasnt really been doing much.