Those four tamers represent the elements of Pandaria: Fire, Water, Earth and Air.
Similar to the pet trainers, once you beat them in an initial quest, they offer a daily with a satchel that can contain the pet version of the Spirit Tamers:
Those are some nice looking pets and the 熊貓人水靈
has a special place in our hearts. He was one of the most important pets in most collections because of the famous "Howl-Bomb" strategy, which however was made impossible in patch 7.0.3.