The Legend of Korra Episode 4, which aired today, contained the first on-screen glimpse of Aang, besides the opening credits and gave a bit more information about what Aang got up to between A:TLA and LoK.
First, here's some pictures of his appearance.
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Apparently, about forty years prior to The Legend of Korra, Aang was forced to face off against another powerful enemy that threatened Republic City. I'm pretty sure that the name of this man was revealed in the episode, but unfortunately, I kept getting interrupted while watching the episode, so I must've missed it.
His appearance was very brief, and near the end of the episode. It is not Spirit!Aang, nor did he speak. But, still, it's a great start.








