There have been countless Avatars over time, appearing in different faces and races, but they have all in essence been the same person. These Avatars, each respectable and memorable in their own right, have a statue in their honor held in the Southern Air Temple's Sanctuary. Although the statues remain nameless, their impact on the world and those who knew them personally have not gone forgotten.
Roku of the Fire Nation was the Avatar before Aang, and reigned for a century. He kept the world in peace until his death, and the Fire Nation's ambition for world domination took flight. Roku's animal guide was a large red dragon with the ability to communicate telepathically by placing one of its whiskers on a person's forehead. There use to be a golden statue of Roku on the top floor of a temple on a cresent-moon shaped island in the Fire Nation, but that temple was destroyed in episode 8, by Roku himself.
Roku has had five appearances in the show; first as a statue and in the clouds of episode 3, then as another statue in episodes 7 and 8, as well as in person/spirit form in ep 8 when he spoke to Aang about Souzen's Comet. In ep 16 he appeared again in person/spirit form to Jeong Jeong in a vision to convince him to teach Aang firebending. And in ep 20, he spoke to Aang in the Spirit World as his reflection in the water.
Kyoshi of the Earth Kingdom was the Avatar sometime before Roku, although the exact time is still debatable. She was born on an island in the southern hemisphere (that later was renamed after her) 400 years ago. She used two fans as weapons and wore an intricate warrior's gown and headset, creating a tradition that is still followed by the female warriors of Kyoshi Island today. She has only appeared in the show twice, as a statue and wall mosaic in episode 3, and as another statue in episode 4.