Kaitou-Saikyou-Zeta
Fire. Air. Water. Earth. All four element of life that came from animals, nature and spirits that have existed far longer than humanity. When the age of human came, they learn the usage of these elements from animals and spirits, and the humans capable of using the element are called as Benders. For centuries, there has always been conflict between human and spirit, until when one human who fused with the Spirit of Light, Raava, and use all four elements, rise to stop the conflict.
The one who mastered all elements is called as Avatar. The Avatar is the one who unite the humanity and the spirit, while keeping the peace in the mortal world. With the end of Avatar Korra's era, a new era of Avatar will soon begin to ensure the peace of the world.
(A/N: Avatar franchise does not belong to me. It belong to the respective owner.)