who had the most natural talent in the history of chess

Natural? A bit of magnus.

Probably some player we've never heard of, who never put the work in to get to GM level.

Among top-level players, I think three stand out for me: Morphy, Capablanca and Tal. But there are also those who say that untrained endgame ability is one of the key markers of a chess talent, and if that's the case then Carlsen and Smyslov have to be seriously considered.

An actual genius does not put up with the fide shenaningans period

this is a very good answer.

adolf anderssen pulled a magnus and proved himself the strongest player in the world when he was like, 21 to 23, back in 1851, so even he could be down on this list. morphy, pillsbury, lasker, capablanca, akiba, tal, spassky, karpov, kasparov, anand, kramnik, ivanchuck, magnus, alireza, and many more

Greco. He had to figure it all out pretty much on his own.

     Of course all the very best players have a tremendous bank of raw talent (it's not certain what that is). Some players devote countless hours over long years to develop that talent, others are more casual. Fischer and Spassky were about equal over most of their careers. Boris was notoriously lazy and Bobby fanatically dedicated (some say crazily obsessive), which benefitted him in the end. The players who reach the top without the grind of endless study are undoubtedly the ones with the most "natural ability".

     Capablanca reportedly learned to play chess as a small child without any instruction, just watching his father play a friend (a strong player) every Sunday. He shocked the two men by pointing out a mistake his father made, got some tutoring, and was soon amazing people by playing and winning simuls against serious adult players. He played very quickly through most of his career, seeming to instantly recognize the best move. He didn't bother with seconds or much preparation in his world-championship matches, and outplayed many opponents in adjourned games when he spent a few minutes in a side room just before the game resumed while his GM-strength opponent had done hours of analysis. As much, probably more innate talent as anyone ever. 

     Mir Sultan Khan, a complete unknown brought from India as a household servant, played in England for a few years (1919-1933) and had tremendous success. He only learned European chess when he reached England but was champion of England three times and held his own vs the world's top players in international tournaments, including a win vs Capablanca. He is frequently cited as the "greatest natural player ever", but learned Indian chess at a young age and was the best player in Punjab before coming West, so his natural ability may be a bit over-estimated.

     Magnus Carlsen started playing a few years later in life than most prodigies but his meteoric rise through all classes of play to win the GM title is unprecedented. He is the youngest person ever to become world champion, and is the highest-rated player ever. Today's availability of chess on the internet makes it easier to study the game, but Magnus has done more with it than anyone else. Should he continue to improve and dominate all comers, he might well be considered the most talented player ever.

     However, probably the greatest natural talent ever was Paul Morphy. There was little chess literature available in his day, so his game came primarily from his own mind. He learned to play at home, was considered the top player in New Orleans by age 10, defeated visiting Hungarian champion Johann Lowenthal at age 12, finished his law degree when he turned 20 (to young to be admitted to the Louisiana bar) and went to New York to win the first US chess championship, then on to Europe,  beating all the top players he faced and astounding everyone with his blindfold simul triumphs. Then he came home and quit chess, considering it too trivial to be is life's work. Many people (including Fischer and Anand) rate him as one of the handful of the game's all-time best players. He came up with new opening innovations, new attacking strategies, and Steinitz and Tarrasch studied his ideas as the basis for the theory of positional play. All in a career of less than three years. And he did it in his spare time.

Morphy and Capablanca are who i think of first but i'd also add Reshevsky to the list.

https://www.chesshistory.com/winter/extra/reshevsky1.html

id like to point out that morphy actually read almost all chess literature that he could get his hands on