Mongke once served under GeneralIroh in the Fire Nation Army. Afterwards, he joined and became the leader of the Rough Rhinos. In 91 ASC, he and the group were responsible for the death of Jet's parents and the destruction of their village.
In spring 100 ASC, the Rough Rhinos had their first encounter with Team Avatar. Mongke mistakenly assumed that Sokka was the Avatar and ordered his team to capture him. When they arrived in the village where Sokka was located, Mongke and the Rhinos ambushed Team Avatar and apprehended Sokka. Aang, Katara, and Toph were still unbound, however, so they used their bending abilities to defeat the Rough Rhinos and force them to flee the town.
Later that spring, Colonel Mongke encountered Avatar Aang and his friends again at their campsite. The Rough Rhinos attempted to kidnap the Avatar; however, their raid was unsuccessful.
That evening, the Rough Rhinos attempted to claim the Earth Kingdom's Chin Village in the name of Fire LordOzai. Mongke and his fellow warriors were defeated in combat once again by Avatar Aang and his friends.
The Rough Rhinos also ambushed Iroh and PrinceZuko, seeking to apprehend them for their traitorous actions. While Iroh appeared happy to see them, even complimenting their singing abilities, Mongke was unmoved and ordered his group to arrest the fugitives. After a brief battle, Zuko and Iroh managed to escape.
Colonel Mongke was a capable firebender and a tough opponent to defeat, especially when fighting alongside the other Rough Rhinos. He was a good tactician and had a knack for singling out weaker Earth Kingdom towns. At one point, he nearly captured the Avatar. Mongke and the rest of the Rough Rhinos were also said to be capable singers.
His name seems to reflect a Mongolian influence. "Mongke" is the name of Genghis Khan's grandson and means "eternal", which makes sense given that Khan himself has been seen as a destructive warmonger.