Roku's earthbending teacher

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.

Opening Sequence
Roku's Earthbending teacher is speculated to be the shadowed Earthebnder in the opening sequence.