Roku

" In my life, I tried to be disciplined and show restraint, but it backfired when Fire Lord Sozin took advantage of my restraint and mercy. If I had been more decisive and acted sooner, I could have stopped Sozin and stopped the War before it started. "

Avatar Roku is the Avatar before Aang. He was apart of the fire nation, but as all avatars he has the abilities to use all four elements. He aids Aang along the way, guiding him to his destiny from the spirit world. His guardian animal was a dragon. He was killed from an overwhelming volcano that he was trying to stop, and was betrayed by his friend Fire Lord Sozin.