Last updated: 04/24/2018
The Wanfu Temple of Tainan, Taiwan worships Sun Wukong in his guise as the Great Sage Equaling Heaven. Most surprisingly, they recognize more than one Great Sage, each with his own function. These include a trinity, three in administrative positions, and an army of dozens of other Monkeys. The idea of multiple Great Sages goes back centuries to an early Ming dynasty (14 to 15th-century) operatic stage play (zaju, 雜劇) by Yang Jingxian (杨景賢) titled Journey to the West (Xiyouji, 西遊記), which predates the similarly named novel by two hundred years. Scene nine of this play sees Monkey introduce himself, his past misdeeds, and his family. He claims to be one of several siblings:
We are five brothers and sisters: my elder sister is Lishan Laomu [離山老母, Venerable Mother of Mount Li], my second sister Wuzhiqi Shengmu [巫支祇聖母, Holy Mother Wuzhiqi]; my older brother is Qitian Dasheng [齊天大聖, Great Sage Equaling Heaven], I myself am Tongtian Dasheng [通天大聖, Great Sage Reaching Heaven], and my younger brother Shuashua Sanlang [耍耍三郎] (Dudbridge, 1970, p. 110). 
Fig. 1 – A modern altar statue of the Lady of Linshui (larger version).
Astute readers will notice a discrepancy with the novel. Sun Wukong is referred to here as the Great Sage Reaching Heaven, while an older brother is known as the Great Sage Equaling Heaven. Sun (2018) suggests the older brother is the result of confusing similar titles given to Monkey during the long history of the story cycle (pp. 44-45). It’s interesting to note, however, that the female siblings have their own history. The Venerable Mother of Mount Li (more commonly written 驪山 and 黎山) was historically worshiped as a deity from at least the Song Dynasty (960-1279), and myths often associate her with the creation/flood-conquering goddess Nuwa (女媧) (Theobald, 2010; Yang & An, 2005, pp. 222-223). Wuzhiqi (also written 無支祁) is a monkey-like flood demon appearing in stories as far back as the Tang dynasty (618-907) (Andersen, 2001). So both sisters are associated with flooding.
Fig. 2 – An artist’s depiction of the six-eared macaque. Fig. 3 – Sun Wukong fighting his double (video).
The Journey to the West novel provides a possible answer to the mystery of the multiple Great Sages. After returning home to the Mountain of Flowers and Fruit in chapter two, Wukong tells his children about his new name:
“My surname is Sun,” replied Wukong, “and my religious name is Wukong.” When the monkeys heard this, they all clapped their hands and shouted happily, “If the great king is Elder Sun, then we are all Junior Suns, Suns the Third, small Suns, tiny Suns—the Sun Family, the Sun Nation, and the Sun Cave!” (Wu & Yu, 2012, vol. 1, p. 130)
This would explain the army of monkey soldiers who do the bidding of the aforementioned trinity.
Additionally, another Great Sage appears in the pious novel Pacification of the Demons of Linshui (Linshui Pingyao zhuan, 臨水平妖傳, c. 17th-18th-cent.). The narrative recounts the miraculous deeds and deification of Chen Jinggu (陳靖姑) (fig. 1), more commonly known as the Lady of Linshui (臨水夫人), a highly popular Fujian and Taiwanese protector goddess of pregnancy and children. The novel depicts the Cinnabar Cloud Great Sage (Danxia Dasheng, 丹霞大聖) as a red-furred, mulberry staff-wielding monkey who, just like Sun Wukong, stole heavenly peaches and survived a turn in Laozi’s furnace. He teams up with another demon to attack the goddess and her heavenly companion, but both are beaten back. The Great Sage is so badly burnt by a magic flaming pearl used by the companion that it takes an entire year for him to heal his wounds. One year later, he resumes his misdeeds and takes on the appearance of a young man, causing so much havoc that the real human is chased from his village. The young man calls on the goddess, who promptly captures the Great Sage and castrates him “in order, she says, to open to him the way of true asceticism stripped of desire, of true wisdom allowing him to obtain the ‘just fruits’, zhengguo [正果]” (Baptandier, 2008, p. 111). After being deprived of his manhood, the novel reveals the Cinnabar Cloud Great Sage to be the “double” of Sun Wukong. He goes on to become an agent of justice charged with conquering demons. 
Fig. 4 – An example of the Three Great Sages from a Lady of Linshui temple (larger version).
I want to briefly mention the idea of the Cinnabar Cloud Sage being Sun Wukong’s double is most likely based on the Six-Eared Macaque (Liu‘er mihou, 六耳獼猴) from chapters 56 to 58 of Journey to the West (fig. 2 and 3).  This demon takes on Monkey’s form, much like the Cinnabar Cloud Great Sage does the young man in the aforementioned novel, and causes all sorts of trouble. When the twins seek the Buddha’s wisdom to tell one from the other, the Enlightened One reveals the fraud to be one of four supernatural primates, the other three being the intelligent stone monkey, the red-buttocked baboon, and the bare-armed gibbon. The demon attempts to flee but is eventually killed by Sun Wukong (Wu & Yu, 2012, vol. 3, pp. 112-116).
A religious tradition in Fujian appears to borrow from both the Yuan-Ming play and the Linshui novel to derive a trinity of familiar Great Sages. These are the red-faced Cinnabar Cloud Great Sage (丹霞大聖), the black-faced Great Sage Reaching Heaven (通天大聖), and the white-faced Shuashua Sanlang (耍耍三郎/爽爽三郎) (fig. 4) (Chinese Monkey God(s)?, n.d.; Wu, n.d.). Therefore, this plethora of Great Sages could have influenced the many venerated in Wanfu temple.
Elliott (1955/1990) describes a Chinese medium in Singapore who channels two of five Great Sages.
According to the current version of the legend, for which no supporting authority can be found elsewhere, there are five Monkey Brothers who may appear when the shen [神, god] is invoked. Each is likely to appear for a number of years before handing over to another brother, unless for any special reason the others have to be consulted. The first Monkey Brother is the wisest and most quiescent of them all. When possessing the dang-ki [童乩, the medium] he can be identified by the manner in which he shades his eyes with his right hand while gazing into the distance. The second Monkey Brother is of fiercer temperament, and can be identified by the manner in which he scratches at his ears as a monkey would. He has a predilection also for eating fire and fruit. The third, fourth and fifth Monkey Brothers are more and more irascible, but there is no detailed knowledge concerning their characteristics since they have never yet appeared. So far it is only the second Monkey Brother who possesses the dang-ki, although the eldest brother is sometimes deferred to in difficult cases and may make a temporary appearance (p. 82).
This shows the concept of multiple Great sages is not restricted to Fujian or Taiwan.
Another possible avenue opens to us thanks to Monkey’s resemblance to the Chinese god Sire Thunder (Leigong, 雷公). Sun Wukong is compared to the weather deity numerous times throughout the novel (Wu & Yu, 2012, vol 3, p. 352, for example). The connection between the two is an old one, for two tales from the early Song Dynasty (960-1279) portray the thunder god as having the form of an ape with flashing, mirror-like eyes (Meulenbeld, 2007, p. 72). These sound very much like Sun Wukong’s fiery eyes and diamond pupils. Most importantly, tales from the same time period refer to the thunder deity having numerous brothers. Their attributes are similar to the aforementioned five Great Sages:
We are five brothers. If you want to hear the sound of thunder, only call Thunder the old, and Thunder two; then you will have an immediate response. But Thunder five is tough and hot-tempered; if there is no urgent business, you must not call him (Meulenbeld, 2007, p. 69).
The concept of five thunder brothers was solidified by the second half of the Song Dynasty and remains a common belief to this day (Meulenbeld, 2007).
1) The name of the youngest brother could be translated as “Shuashua, the third son” considering the god Erlang (二郎) is literally the “Second Son”. Shuashua is after all the third of three sons.
2) See chapter four in Baptandier (2008) for a complete description of the life and deeds of the Cinnabar Cloud Great Sage.
3) Anthony Yu suggests the concept of six ears “may have been derived from the common Buddhist saying, ‘The dharma is not to be transmitted to the sixth ear [i.e., the third pair or person] 法不傳六耳'” (Wu & Yu, 2012, vol. 3, p. 387 n. 7).
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Baptandier, B. (2008). The Lady of Linshui: A Chinese Female Cult. Stanford, Calif: Stanford University Press.
Chinese Monkey God(s)? – What You Don’t Know. (n.d.). Retrieved from http://taoist-sorcery.blogspot.tw/2015/08/chinese-monkey-gods-what-you-dont-know.html
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Elliott, A. J. (1990). Chinese Spirit-Medium Cults in Singapore. London: The Athlone Press. (Original work published 1955)
Meulenbeld, M. R. E. (2007). Civilized Demons: Ming Thunder Gods from Ritual to Literature (Doctoral dissertation). Available from ProQuest Dissertations and Theses database (UMI No: 3247802).
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Wu, C., & Yu, A. C. (2012). The Journey to the West (vol. 1-3). Chicago, Illinois: University of Chicago Press.
Wu, J. (n.d.). The Three Monkey Sages of Lin Shui Palace. Retrieved from http://javewutaoismplace.blogspot.tw/2014/01/three-monkey-sages-of-lin-shui-palace.html
Yang, L., & An, D. (2005). Handbook of Chinese mythology. Santa Barbara, Calif.: ABC-CLIO.