...and how did he get his powers?
My theory: Amon (who was known as Yukon at one point) threatened Republic City 42 years before the start of "Korra." I believe he was a bender, and from his name, a water bender. When a confrontation between Aang and Yukon ensued, Aang took his bending away. Yukon escaped from being imprisoned, and Aang made the mistake of believing that with no bending, Yukon could not hurt anyone anymore. After all, former Fire Lord Ozai had never hurt anyone after his bending had been taken away. However, Yukon was furious, and tried to understand how his bending was taken away. In the process, he went to the spirit world, where I believe he met Koh, who gave him the ability to take other people's bending away. If he couldn't bend, neither could anyone else, especially the Avatar.
As for what happened to Zuko's mom... I have no idea! Bryan and Mike are TROLLS!
This is my theory! No stealing!
What do you think?