Does Sun Wukong worship predate Journey To The West?
The worship of Sun Wukong is complicated. Fujian, China, the home of our hero's cult, is known to have worshiped monkeys in general as far back as the Tang Dynasty. A prime example is the "Spirit protecting hills and woods" (Bao shanlin shen, 保山林神). As the story goes, the enraged monkey-spirit was appeased with worship after its mortal body had been killed and taxidermied to make an idol.
A Song-era story mentions an evil monkey-spirit titled the "Great Sage Equaling Heaven" (Qitian dasheng, 齊天大聖; "GSEH" hereafter), just like Wukong. But he is portrayed as a fiendish, wife-kidnapping sorcerer, while Monkey's Song-era antecedent, the "Monkey Pilgrim" (Hou xingzhe, 猴行者), from the 13th-century JTTW, is cast as a white-robed scholar immortal. (Interestingly, though, this precursor is given the title "Great Sage Steel Muscles and Iron Bones" (Gangjin tiegu dasheng, 鋼筋鐵骨大聖) at the end of his story arc.) If the local Fujian people considered the Song-era GSEH a real threat, I could see them also attempting to appease him through worship.
Having said that, it's interesting to note that a Fujian shrine dedicated to both the GSEH and the "Great Sage Reaching Heaven" (Tongtian Dasheng, 通天大聖) appeared by the 14th-century. These two figures eventually appeared in Yuan-Ming zaju and puppet plays, by which time Sun Wukong had already become associated with the GSEH title. I'm not sure when the switch happened, though. This then raises the question: did the switch happen later, leading to Monkey being assimilated into the GSEH's cult and taking over the main focus of worship, or did it happen earlier and the GSEH title was just absorbed by Wukong and his already existing cult?
But either way, I can say with confidence that Monkey and the other pilgrims were venerated prior to the novel. This is because they are all described as Buddhas that have left the world in the Five Books and Six Volumes (Wubu liuce, 五部六冊; 1509), a sectarian Buddhist text by the amazingly influential Luo Menghong (羅夢(孟)鴻, 1442–1527). This religious work predates JTTW by 83 years! This might be one of the reasons why the pilgrims receive a promotion in spiritual rank in chapter 100.
