Avatar: Who The Four Benders Are In Legend of Korra's Opening Credits
Just like in the original series, The Legend of Korra's opening credits show four benders performing the world's four bending techniques, but their identities have been shrouded as silhouettes. Throughout Avatar: The Last Airbender's run, as well as in comics, graphic novels, and of course, The Legend of Korra, various sub-bending techniques have been discovered, including Energybending, Bloodbending, and more - but the original, core four will always be Airbending, Earthbending, Firebending, and Waterbending.
Those four bending powers were highlighted in the opening credits for Avatar: The Last Airbender - Master Pakku represented Waterbending, Sud represented Earthbending (despite not appearing until much later on), Azula represented Firebending (again, despite not appearing until the end of season 1), and an unknown character represented Airbending, though many people have believed that person to be Aang. The Legend of Korra continued this tradition with four benders of its own, but the people in the opening credits were different - as was the order in which they appeared.
The four benders in The Legend of Korra's opening credits were Kyoshi (Earthbending), Roku (Firebending), Aang (Airbending), and Korra (Waterbending) - in that particular order. To the uninitiated, these may seem random, but there's a level of nuance to the reason these four benders were chosen for Legend of Korra's opening credits and the order in which they were shown, especially Korra being the final one.
To some extent, the identity of the next Avatar is randomized, but everyone's aware of which nation the spirit will be reborn in; there's a cyclical system to it. The Airbenders were the previous nation to produce the Avatar (Aang) - in fact, this is why the Fire Nation wiped out all the Airbenders in the first place - and so, the Waterbenders were the nation next in line. This cycle is represented in the opening credits: earth, fire, air, and then water. But there's more to the people who represent these elements in the introduction.
While the order of the elements shown embodies the Avatar Cycle, the benders themselves are the previous Avatars. Kyoshi served as the Avatar from 312 BG to 82 BG, and then she was succeeded by Roku, who served from 82 BG to 12 BG. After him came Aang, whose tenure as the Avatar lasted from 12 BG to 153 AG (thanks to him spending 100 years hibernating inside an iceberg). Korra is the most recent Avatar, who was born in 153 AG, which is why she appears last in Legend of Korra's opening credits.