Oogi is a major character from the TV series, The Legend of Korra.
Oogi is Tenzin's flying bison, who was founded by Aang after he thought that the species are extinct due to Air-Bender genocide. Oogi appeared in the first episode of The Legend of Korra. The ones riding on him are Tenzin and his children. Oogi appeared in the rest of the episodes as a loyal companion of Tenzin.
Since Oogi is an air bison, he strongly resembles Appa, but the difference is that Oogi has darker fur, since he is a different subspecies of air bison.
Just like Appa, in order to fly, the name is first called, then there is a Yip yip. He is also able to understan human language, since he obeys commands.