There may be no more controversial film in the Marvel Cinematic Universe than Iron Man 3. The film puts a significant twist on one of Iron Man's most well known adversaries from the comics, in a move that is either loved for the way it subverted expectations or hated for the way it subverted expectations.
However, for fans who were upset that they never got to see "real" Mandarin in Iron Man 3, it seems they may have a chance, as Marvel Studios chief Kevin Feige has confirmed that, in some way, the 10 Rings terrorist organization, and its leader the Mandarin will be dealt with in the future of the MCU.
In Iron Man 3 we were introduced to Ben Kingsley as a character being called the Mandarin. One of Iron Man's best known villains, The Mandarin wears 10 rings on his fingers which give him special power because of the alien technology that formed them.
Kingsley was great in the role of the Mandarin, possibly perfect casting, but it turned out that the whole thing was a dodge, as the movie eventually revealed that Kingsley's character was actually that of an actor named Trevor Slattery who had been hired by Guy Pierce's Aldrich Killian. The entire concept of the Mandarin was a front to distract from Killian's actual plans.
However, the frustrations of fans who wanted to see the more classic version of the Mandarin were given a brief moment of hope when the Marvel One Shot All Hail The King was released on the Blu-ray of Thor: The Dark World. The short film shows Trevor Slattery in prison, where he is kidnapped by a member of the 10 Rings organization, and is told he will be taken to see the man whose name was stolen. The Mandarin is real, and he's unhappy.
We've heard little from the 10 Rings and nothing from the Mandarin since then in the MCU but during a recent Reddit AMA Feige was asked if there were any plans to bring them back, and Feige simply replied, "yes."
Feige doesn't say a word beyond the confirmation, so we have no clue how the Mandarin could be coming to the MCU, but rumors and fan theories have suggested the character could play a role in the Shang-Chi movie, which is one of the few titles confirmed by Marvel to be part of Phase 4. Considering the villain is typically presented as Asian, and this is supposed to be "real" version of the character, it would make some sense.
On the one hand, as somebody who loved the Iron Man 3 twist because of the way it showed the MCU wasn't married to convention, I was honestly a little disappointed when All Hail the King came out and walked some of it back. Having said that, if the real Mandarin is a strong enough character, then it doesn't really matter.