Digimon Sovereigns

The Sovereigns are fictional characters that appear in the anime series, Digimon. There are four Sovereigns: Azulongmon (Qinglongmon), Zhuqiaomon, Baihumon, and Ebonwumon (Xuanwumon). They themselves serve under Fanglongmon.

Origin of Names
Each of the Sovereigns is portrayed as ruling over a quarter of the Digital World. This ties into their names, which are all based on Chinese astronomy. In Chinese, the four quadrants of the sky (east, west, north, and south) are known as Celestial Temples, with each given names: Qinglong, Zhu Que, Bai-hu, and Xuanwu. Qinglong means "Azure Dragon," Zhu Que means "Red Bird," Bai-hu means "White Tiger," and Xuanwu means "Black Tortiose."

The Japanese based the Four Gods of Kyoto on the chinese Ssu Ling, deriving the names Seiryu, Suzaku, Byakko, and Genbu from them.

Digimon 02
While they were referenced, only Azulongmon made a appearence in the series to play a important role in the show.

Digimon Tamers
The four Sovereigns played an important role in Digimon Tamers. Zhuqiaomon was responsible for the Devas, prompting the main cast to enter the Digital World. He is the first of the four to appear, battling the Tamers until stopped by Azulongmon. Later on, Baihumon and Ebonwumon met with Azulongmon and Zhuqiaomon on how to handle the D-Reaper situation and helped Calumon release the Shining Digivolution which Digivolved every Digimon everywhere to their Mega forms to help the Sovereign. In the final battle against the D-Reaper, they reappeared to help drag the Cable Reaper back into the Digital World during Operation: Doodlebug.