Actually, I'll just outline the basic context/premise here (enough to follow the intro scene) for anyone interested:
Journey to the West was basically about a Buddhist monk who helped reform three would-be-villains who were punished by the gods for their crimes by being assigned to be the monk's bodyguards on this epic journey that would result in them becoming "buddhas" themselves. One's a bandit, one's a love-sick borderline sex predator, and one is Wukong, who's basically this all-powerful somewhat Homelander-esque (well, a carefree/playful version) child-brained ego-maniac/troublemaker who just wants the freedom to do whatever he wants and can't be stopped because he becomes so over-powered and immortal (that's why his dialogue sometimes sounds villainous-- it's like his "Id" leaking out). A "slave crown" with the ability to activate headaches is given to the Monk (who has no physical abilities) in order to prevent Wukong from rebelling against his assignment (this makes an appearance in the intro of Black Myth with no explanation). The game takes place after their journey succeeds.
Before all this happens, in the prologue of the original story, Wukong becomes the king of the normal monkeys and mischiefs his way towards becoming progressively more powerful/immortal (by eating/stealing things that grant him these abilities), to the point where the celestial gods take notice and become concerned about him being a threat to world order. So they keep him under their thumb/out of trouble by giving him god-like empty titles that nobody takes seriously (just to keep him occupied in heaven, away from doing anything catastrophic to the world). After he realizes this and gets fed up with their rules and manipulation, he throws the mother of all temper tantrums over it, and it escalates until eventually he goes on a one-man-war against the entire celestial forces (with his monkeys getting hurt in the crossfire-- he taught them to talk/fight, btw, otherwise they'd be normal monkeys). This is the event that he gets punished for with the journey.
It looks like in the intro of Black Myth, history repeats itself after he comes back from the journey, complete with a nearly identical epic rematch.
(come to think of it, thematically, that's a bit annoying, because it just completely undoes his reformation like it never mattered)
Edit: Also, in case anyone's confused about the beginning of Chapter 1, which is still kind of a mystery, it sounds like Wukong was crushed/killed/dispersed into the items you're looking for. Neither the old monkey nor the monkey you end up playing as (who seems to have less personality) are Wukong. Wukong was born out of a giant stone, which is why the old one was brandishing it (not sure if significant). Also not sure how/why the player character has all his abilities. Reincarnation? Or just a random monkey he taught with potential (normally they're weak disposable fighters with sticks but no magic)? Clearly not immortal like Wukong, but did they just give him his magical staff after he "died"?