Sokka
In "Sokka's Master" (the 4th episode of third season) Sokka expresses self-doubt that he is not as useful to the group as his companions. Inspired by his friends' encouragement, he seeks out a master to learn the sword. Rather than fighting with brute force and flawless technique, Sokka's creativity and heterodox approach to things are the cornerstones of his technique, and his master claims that in time Sokka will be a superior swordsman. As he departs, his master gives him a game piece that was previously established as a sign of connection to the secret society known as the Order of the White Lotus.