"He is Valoran's first fully functioning homicidal comic; he jests until someone dies, and then he laughs." That is the second sentence of Riot's biography of Shaco, and it is also the only thing in it stated as fact. The rest is a list of what people believe. For a character with a Universe page in the world of Runeterra, that is unusual; for a character the page itself calls an enigma, it may be the point.
Who they are
The biography is short and it is honest about why. Nobody agrees where the Demon Jester came from, and Shaco offers no details of his own. It gives three beliefs and grades them. A popular one holds that he is not of Runeterra at all, a thing from a dark and twisted world. Others say he is the demonic manifestation of humanity's dark urges, and therefore cannot be reasoned with. The one the text calls most plausible is the dullest: he is an assassin for hire, left to his own lunatic devices until his services are needed.
What the biography does commit to is behaviour. Shaco is cunning, and has evaded every authority that wanted him for questioning over some horrendous, law-breaking atrocity. The text notes the oddity itself, that a figure so malevolent is allowed to remain at large, and offers no explanation. He is terrifying and elusive, and he is most often seen where madness can openly reign.
That is the whole of it. There is no birthplace, no first murder, no named victim, no named employer and no named enemy. Where other biographies in this stretch of the roster run to a thousand words of family, war and transformation, Shaco's runs to a paragraph that refuses to settle his nature and a closing line that tells you where to look for him. The gaps are not an oversight the site can fill from elsewhere; they are what Riot published.
Where they belong
No region on Riot's faction pages. The biography places him in Valoran, the continent, and nowhere narrower; wherever madness reigns is not a coordinate. No race is listed, and the text's three theories (an outsider, a demon, a man for hire) are the only classification on offer.
Two related champions appear in our data, Fiddlesticks and Nocturne, and neither is named in the biography. Riot's page links the three; the text gives no relationship to repeat, and we do not supply one.
In the Riot MMO, as a guess
This is speculation. Shaco is a boss, and the rare kind that should not be found on a map: a character defined by turning up where madness is loose is a random encounter, the thing that appears in a zone already going wrong and leaves before the authorities arrive. He cannot be a quest-giver, since the biography gives him no wants and no side, and a name on a wall would contradict a text that says he is still at large. The most plausible theory, an assassin for hire, even suggests who might send him. He belongs to no hub, which fits a boss that visits every one of them. The wider sorting of the roster is in will champions be playable, NPCs or bosses.
What we do not know
What he is. The biography offers three theories, ranks one as most plausible, and confirms none.
Whether the game's era finds him alive. The text carries no date, no age and no origin, so the period chosen in when is the Riot MMO set has nothing to anchor to; a figure who may not be of Runeterra at all does not obviously age with it, and Riot has not said.