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 Pandaren Water Spirit 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.
Xu-Fu can scan this section for the most suitable strategies according to your preferences and show the required pets.
Depending on the amount of fights in the section, this can take up to a minute to process.