Sud

My Earthbending master, Sud, was uncompromising, stubborn, and blunt.

Roku's Earthbending teacher taught him Earthbending when he was a young Avatar from the Fire Nation.

History
Not much is known about this character, however, we do know that he was a citizen of the Earth Kingdom. He trained Avatar Roku in the art of Earthbending, teaching him the techniques of a master Earthbender. Roku eventually mastered Earthbending under his tutelage, and beat his teacher in a race up a mountain, while surfing of the earth. By the time his teacher had reached to top of the hill, Roku was already sitting there brewing a pot of tea. The teacher laughed, and they sat down to enjoy the hot beverage. By the time Roku finished his training, he was a fully realized Avatar, able to control all four elements at will. Roku seemed to enjoy learning Earthbending, as it was not his opposite element.