The opening theme features the most recent Avatars performing their respective bending: Earth - Kyoshi, Fire - Roku, Air - Aang, and the current Avatar, Korra, is seen waterbending.
Seychelle Gabriel, who voices Asami Sato in The Legend of Korra, also played Princess Yue, who was love interest of Sokka, in the live action movie "The Last Airbender".
The character Mako is actually named after the actor who played Uncle Iroh for the majority of Avatar: The Last Airbender. Sadly Mako passed away before the show ended.