King could be better, but emperor also OK. See Wikipedia page for Dali.Originally Posted by JamesG
South Emperor's surname Duan, given name Zhixing, was a real person in history. He ruled the Kingdom of Dali from 1172 to 1199.
In the history, many emperors of Dali became monks, but Duan Zhixing was not among them, he died of illness in 1199. But the novel says Duan Zhixing not real died in 1199 (Guo Jing borned in November 1200), but became a monk and lived out of the world. So the novel exactly matches the real history.