In the game, the Macaque Chief (Perhaps it would be more reasonable to translate it as red−rumped mandril) is one of the four special monkeys mentioned in the classic Chinese novel "Journey to the West." The red−rumped mandril, isn't a specific monkey but rather a type of monkey.

Description in the Original Text

In Chapter 3 of "Journey to the West," four old monkeys from Mount Huaguo: two red−rumped mandril and two magic−armed gibbon, guide the Monkey King to the Kingdom of Aolai to obtain weapons for the monkeys to practice with. Later, they are appointed as the Four Generals: the two red−rumped mandril are named Marshal Ma and Marshal Liu, while the two magic−armed gibbon are named General Beng and General Ba.

In Chapter 58 of "Journey to the West," the Buddha mentions the existence of four special monkeys, who do not belong to any of the ten categories of creatures:

• The first kind is the intelligent stone monkey, he can do all kinds of transformation, knows all about the seasons of Heaven and earthly advantages, and can move the stars and their constellations about.
• The second kind is the red−rumped mandril that knows all about the Yin and the Yang and human affairs, can go into or out of anywhere, and knows how to prolong its life and avoid death.
• The third kind is the magic−armed gibbon that can catch the sun or moon, shrink mountains, see what is auspicious and what is not, and fool around with heaven and earth.
• The fourth kind is the six−eared macaque which has wonderful hearing and perception. It knows about the past and the future and understands all creatures.

These four kinds of ape do not come within any of the ten categories and are not listed among the creatures that live between heaven and earth. I can see that the false Sun Wukong is just such a six−eared macaque. Wherever he stands he can know what is happening hundreds of miles away and hear everything that is said. That is why he has such wonderful hearing, brilliant perception, and knowledge of the past, the future, and all beings; that is why he looks and sounds just like Wukong. He is a six−eared macaque.

Most of this article's translations come from: https://www.reddit.com/r/BlackMythWukong/comments/1eh9oq4/one_small_detail_everyday_day_8_the_redrumped/