Last updated: 02-26-2022
Sun Wukong faces his evil double, the Six-Eared Macaque, in chapters 56 to 58 of Journey to the West (Xiyouji, 西遊記, 1592, JTTW hereafter). After the twin Mind Monkeys battle their way to the Western Paradise, the Buddha reveals the doppelganger’s true identity, noting that he and Monkey are two of four celestial primates (hunshi sihou, 混世四猴, lit: “four monkeys of havoc”) with amazing abilities:
“The first,” said Tathagata, “is the Stone Monkey of Numinous Wisdom,  who
Knows transformations, Recognizes the seasons, Discerns the advantages of earth, And is able to alter the course of planets and stars.The second is the Red-Buttocked Horse Monkey, who
Has knowledge of yin and yang, Understands human affairs, Is adept in its daily life And able to avoid death and lengthen its life.The third is the Tongbi Gibbon, who can
Seize the sun and the moon, Shorten a thousand mountains, Distinguish the auspicious from the inauspicious, And manipulate planets and stars.The fourth is the Six-Eared Macaque who has
A sensitive ear, Discernment of fundamental principles, Knowledge of past and future, And comprehension of all things.These four kinds of monkeys are not classified in the ten categories [of life], nor are they contained in the names between Heaven and Earth. As I see the matter, that specious Wukong must be a six-eared macaque, for even if this monkey stands in one place, he can possess the knowledge of events a thousand miles away and whatever a man may say in that distance” (Wu & Yu, 2012, vol. 3, p. 115).
In this article, I would like to explore all mentions of these magical creatures in the novel. I will focus more on the second and third primates as I’ve already written extensively about the first and fourth kind.
1. Stone Monkey
There isn’t much to write about the “Stone Monkey of Numinous Wisdom” (Lingming shihou, 靈明石猴) (fig. 1) as it’s clearly Sun Wukong. The term lingming (靈明) can also be translated as “Numinous Luminosity”. Both refer to spiritual wisdom. This explains why Sun Wukong attains so much power after only three years of spiritual cultivation.
Fig. 1 – A poster of the Stone Monkey of Luminous Wisdom from the film “Four Monkeys”. The name has since been changed. See update 02-20-22 below.
2. Horse Monkey and Gibbon
I’m grouping these two together because they share a close association in JTTW. The Chinese term for “Red-Buttocked Horse Monkey” (Chikao mahou, 赤尻馬猴) (fig. 2) appears three times in the novel, while “Horse Monkey” (馬猴, mahou) only appears once (see here).  The term “Tongbei Gibbon” (Tongbei yuanhou, 通背猿猴) appears three times, while the interchangeable term “Tongbi Gibbon” (Tongbi yuanhou, 通臂猿猴) appears once (see here and here) (fig. 3).  The term “ape” or “gibbon” (yuanhou, 猿猴) appears 16 times (see here), and it’s even used to refer to Monkey. For example, a poem in chapter seven calls him “The Great Sage, Equal to Heaven, a monstrous ape” (Qitian dasheng yuanhou guai, 齊天大聖猿猴怪) (Wu & Yu, 2012, vol. 1, p. 191). The horse monkey and gibbon are surprisingly listed among the Monkey King’s retinue:
The Handsome Monkey King thus led a flock of gibbons [猿猴], macaques, and horse monkeys [馬猴], some of whom were appointed by him as his officers and ministers (Wu & Yu, 2012, vol. 1, p. 106).
It’s actually the gibbon who reveals the truth of spiritual beings escaping the hand of death, setting Monkey on his quest for immortality:
From among the ranks a tongbei gibbon [通背猿猴] suddenly leaped forth and cried aloud, “If the Great King is so farsighted, it may well indicate the sprouting of his religious inclination. There are, among the five major divisions of all living creatures, only three species that are not subject to Yama, King of the Underworld.” The Monkey King said, “Do you know who they are?” The monkey said, “They are the Buddhas, the immortals, and the holy sages; these three alone can avoid the Wheel of Transmigration as well as the process of birth and destruction, and live as long as Heaven and Earth, the mountains and the streams.” “Where do they live?” asked the Monkey King. The monkey said, “They do not live beyond the world of the Jambudvipa, for they dwell within ancient caves on immortal mountains.” When the Monkey King heard this, he was filled with delight, saying, “Tomorrow I shall take leave of you all and go down the mountain. Even if I have to wander with the clouds to the comers of the sea or journey to the distant edges of Heaven, I intend to find these three kinds of people. I will learn from them how to be young forever and escape the calamity inflicted by King Yama.” (Wu & Yu, 2012, vol. 1, p. 131).
Apart from this, chapter two casts both the gibbon and horse monkey as knowledgeable elders:
As they were speaking, four older monkeys came forward, two horse monkeys with red buttocks [赤尻馬猴] and tongbei gibbons [通背猿猴]. Coming to the front, they said, “Great King, to be furnished with sharp-edged weapons is a very simple matter:’ “How is it simple?” asked Wukong. The four monkeys replied, “East of our mountain, across two hundred miles of water, is the boundary of the Aolai Country. In that country there is a king who has numberless men and soldiers in his city, and there are bound to be all kinds of gold, silver, copper, and iron works there. If the great king goes there, he can either buy weapons or have them made (Wu & Yu, 2012, vol. 1, p. 131).
Later in the chapter, they are appointed officers:
The Monkey King made the four old monkeys mighty commanders of his troops by appointing the two horse monkeys with red buttocks [赤尻馬猴] as marshals Ma [馬] and Liu [流], and the two tongbei gibbons as generals Beng [崩] and Ba [芭] (Wu & Yu, 2012, vol. 1, p. 138).
These primates are mentioned in a few other chapters (see here and here).
Fig. 2 & 3 – “Four Monkeys” posters of the Red-Buttocked Horse Monkey and the Tongbi Gibbon.
2.1. True Identity?
Anthony C. Yu (Wu & Yu, 2012) calls the horse monkey a “baboon” (vol. 3, p. 115, for example), likely based on the common image of the primate having a red bottom. And while searching “馬猴” does pull up images and articles about the Mandrill, a large, colorful cousin of the baboon (example), I can’t find any reliable historical sources linking the animal with the term. Having said that, this book associates it with the ancient Chinese practice of putting monkeys in horse stables (majiu husun, 馬廄猢猻) to ward off equine sicknesses, making it a “horse’s monkey”. This naturally has connections to Sun Wukong’s time as the Bimawen, or keeper of the heavenly horses. This is the most convincing explanation for the horse monkey that I’ve seen, but I’ll make sure to update the article if any other plausible reasons arise. As for the red bottom, this is likely the sexual swelling of females. I’ll spare you a picture; just imagine a bright pink pumpkin that’s about to explode.
The gibbon and macaque (see below) are real world animals. For more information on Chinese views of the gibbon, please see this archived book.
3. Six-Eared Macaque
I’ve already written an article exploring the literary and religious origins of the “Six-Eared Macaque” (Liu’er mihou, 六耳獼猴). One scholar suggests that his true identity is Monkey’s sworn brother, the Macaque King (Mihou wang, 獼猴王) (Lam, 2005, p. 168). It’s important to note that this character cavorts with Sun on the Mountain of Flowers and Fruit (Wu & Yu, 2012, vol. 1, pp. 156-157, for example).
Fig. 4 – A “Four Monkeys” poster of the Six-Eared Macaque. This version wields swords unlike his staff-brandishing literary counterpart.
4. Home of the Four Primates?
The above information shows that, at one time or another, all four of the celestial primates are present on the Mountain of Flowers and Fruit. The Stone Monkey of Numinous Wisdom (a.k.a. Sun Wukong) is born and lives as a king on the mountain. The Red-Buttocked Horse Monkey and the Tongbei/bi Gibbon serve as his advisors and officers. And the Six-Eared Macaque becomes his sworn brother and often visits him there. This might suggest that the Mountain of Flowers and Fruit is the home or even birthplace of all four primates. If one magic primate can be born there, then all of them can.
Here’s a four minute preview for the upcoming film King of Havoc: Rise of the Great Sage (Hunshi zhi wang: Dasheng jueqi, 混世之王：大圣崛起, 2022). The Six-Eared Macaque appears in figure four wielding swords. This same character takes part in the trailer but is called the Macaque King, thereby referencing the aforementioned theory that he is Six Ears.
One thing I forgot to mention is that one passage suggests ALL four celestial primates are present on the Mountain of Flowers and Fruit in Sun’s youth:
The Handsome Monkey King thus led a flock of gibbons [yuanhou, 猿猴], macaques [mihou, 獼猴], and horse monkeys [mahou, 馬猴], some of whom were appointed by him as his officers and ministers (Wu & Yu, 2012, vol. 1, p. 106).
There’s the Monkey King (Stone), gibbons (Tongbi/bei), macaques (Six Ears), and horse monkeys (Red-Buttocked).
Also, user Phantom86d left an astute comment suggesting that the four magical primates are not part of the 10 categories of life—as stated by the Buddha in the introduction—”[b]ecause Wukong erased their names from the book of Life and Death”. This refers to chapter three when Sun inks out his name and those of all other primates when his immortal soul is mistakenly summoned to hell. It’s important to remember that he had his own, separate book (Wu & Yu, 2012, vol. 1, p. 140), so the other magical primates likely had theirs.
Thanks to this dictionary, I learned that one late-Qing source, New Dialect (Xinfangyan, 新方言, early-20th-c.), associates “horse monkey” (mahou, 馬猴) with various iterations of Chinese terms for macaque monkeys:
“Bathing monkey” (muhou): “mother monkey” (muhou); mother monkey (muhou): “full monkey” (mihou) – these are called “horse monkey” (mahou), the sound of each one changing [in turn].
沐猴：母猴；母猴：彌猴，令人謂之馬猴，皆一音之轉。(the original doesn’t have punctuation)
This article explains that the second term refers not to a female primate but a macaque. The Annotation of the Shuowen jiezi (Shuowen jiezi zhu, 說文解字注, 1815) reads:
“Mother monkey” (muhou) is the name of the beast, not the female. “Bathing monkey” (muhou) and “full monkey” (mihou) are changes in dialect. The characters are wrong.
The Compendium of Materia Medica (Bencao gangmu, 本草綱目, 1596) traces the etymology of “bathing monkey” (muhou, 沐猴):
The monkey likes to wipe its face as if bathing (mu), so it is called a “bathing (monkey)”. Later generations mistook this mu for “mother”, and then mother for “full” (mi). The meaning is lost as errors compound.
It then directly connects muhou (母猴) to stable monkeys:
The Shuowen says: The characters (for macaque) look like “mother monkey” (muhou), but it’s a “bathing monkey” (muhou, i.e. macaque), not a female. Since a macaque resembles a hu-barbarian, he is also called hu-sun “grandson of a barbarian”. The Zhuangzi calls him ju. People who raise horses keep a macaque in the stables, which will ward off horse-diseases. The Hu barbarians call a macaque ma–liu, in Sanskrit books he is called Mo–si–zha (makaṭa). 
The section later explains how macaques (muhou, 母猴) help the horses:
The Classic of Horses states: Domesticated macaques (muhou) used in horse stables help avoid horse diseases [lit: bimawen]. Their monthly menstruation runs onto the grass, and once the horses eat it, they will never be sick.
1) I will be altering Yu’s (Wu & Yu, 2012) translation from this point forward to make it more accurate.
2) Ctext shows the term “Great Horse Monkey” (Da mahou, 大馬猴) pops up in chapter 28 of Dream of the Red Chamber (18th-century). It’s used to symbolize something worse than an immoral husband that would ravage a young maiden:
Next came Xue Pan. “Is it for me to speak now?” Xue Pan asked.
“A maiden is sad…”
But a long time elapsed after these words were uttered and yet nothing further was heard.
“Sad for what?” Feng Ziying laughingly asked.
“Go on and tell us at once!”
Xue Pan was much perplexed. His eyes rolled about like a bell.
“A girl is sad…” he hastily repeated. But here again he coughed twice before he proceeded.
“A girl is sad,” he said:
“When she marries a spouse who is a libertine.”
This sentence so tickled the fancy of the company that they burst out into a loud fit of laughter.
“What amuses you so?” shouted Xue Pan, “is it likely that what I say is not correct? If a girl marries a man, who chooses to forget all virtue, how can she not feel sore at heart?”
But so heartily did they all laugh that their bodies were bent in two.
“What you say is quite right,” they eagerly replied. “So proceed at once with the rest.”
Xue Pan thereupon stared with vacant gaze.
“A girl is grieved…” he added.
But after these few words he once more could find nothing to say.
“What is she grieved about?” they asked.
“When a huge horse monkey [大馬猴] finds its way into the inner room,” Xue Pan retorted (Cao & Joly, 1892, p. 62).
3) These are hard to translate terms referring to the belief that the long, agile arms of the gibbon were somehow connected (i.e. tongbi, 通臂), possibly passing through the back (i.e. tongbei, 通背) (Gulik, 1967, p. 92-93). It’s interesting to note that each are associated with a style of ape-based Chinese boxing.
Cao, X., & Joly, H. B. (1892). Hung Lou Meng: Or, The Dream of the Red Chamber; a Chinese Novel – Book 2. Hongkong: Kelly & Walsh.
Gulik, R. H. (1967). The Gibbon in China: An Essay in Chinese Animal Lore. Leiden: E.J. Brill.
Lam, H. L. (2005). Cannibalizing the Heart: The Politics of Allegory and The Journey to the West. In E. Ziolkowski (Ed.). Literature, Religion, and East/West Comparison (pp. 162-178). Newark: University of Delaware Press.
Wu, C., & Yu, A. C. (2012). The Journey to the West (Vols. 1-4) (Rev. ed.). Chicago, Illinois: University of Chicago Press.