The Hero Wars drink from many sources: the Illiad, the Mahabharata, the Shahnameh... But there is one 16th-Century Chinese novel which, to me and without having read it, seems to be one of the closest things to the Hero Wars that exist in classical literature, and sadly I don't think I'll ever have it in my hands. Ladies and gentlemen, may I present to you: Investiture/Creation of the Gods (Fengshen Yanyi).
From the Wikipedia:
The novel is a romanticised retelling of the overthrow of King Zhòu, the last ruler of the Shang dynasty, by Ji Fa, who would establish the Zhōu dynasty in its place. The story integrates oral and written tales of many Chinese mythological figures who are involved in the struggle as well. These figures include human heroes, immortals, and various spirits (usually represented in avatar form, such as vixens and pheasants, and occasionally as inanimate objects such as a pipa).
Bewitched by his concubine Daji, who is actually a vixen spirit disguised as a beautiful woman, King Zhou of Shang oppresses his people and persecutes those who oppose him, including those who dare to speak up to him. Ji Fa (King Wu of Zhou), assisted by his strategist Jiang Ziya, rallies an army to overthrow the tyrant and restore peace and order. Throughout the story, battles are waged between the kingdoms of Shang and Zhou, with both sides calling upon various supernatural beings – deities, immortals, demons, spirits, and humans with magical abilities – to aid them in the war. Yuanshi Tianzun ("Primeval Lord of Heaven") bestows upon Jiang Ziya the Fengshen Bang, a list that empowers him to invest the gods of Heaven. The heroes of Zhou and some of their fallen enemies from Shang are eventually endowed with heavenly ranking and essentially elevated as gods, hence the title of the novel.
Come on, I can't be the only one who thinks of the Red Emperor of the Lunar Empire vs. King Argrath of Sartar while reading about this King Zhou of Shang vs. Ji Fa of Zhou conflict.
Sadly, this thing is out of print and expensive as hell, but for every Gloranthaphile lucky enough to find and afford it I think it's worth of checking out.