Liu Heita
Luo Cheng's stories in this novel were mostly based on stories of Luo Shixin (罗士信) in the history. Luo Shixin was a young general in late Sui and early Tang dynasty. He started his career as a cavalry guard, and then he took part in Wagang Fort. At last he joined Tang Dynasty's force and helped Li Yuan and Li Shimin with unifying the country. He was also killed during a battle against Liu Heita, like Luo Cheng did in the novel. One thing needs to be clarified: in some versions of the novel, there is also a character called Luo Shixin. However, that character is totally different from Luo Shixin in the history. That is just a different role in the novel.