WARNING: The following contains spoilers for Shang-Chi and the Legend of the Ten Rings, now in theaters.
When Tony Leung joined the cast of Shang-Chi and the Legend of the Ten Rings, he was announced as the Mandarin, a supervillain typically associated with Iron Man. However, Leung's Wenwu reveals that the title actually belongs to a different antagonist in the Marvel Cinematic Universe: Aldrich Killian, played in Iron Man 3 by Guy Pearce.
In the 2013 movie, actor Trevor Slattery (Ben Kingsley) was hired to play a merciless terrorist, unwittingly taking credit for explosions caused by Killian's Extremis experiments. Then, in the Marvel One-Shot All Hail the King, Slattery learns that Killian co-opted the iconography of a criminal organization called the Ten Rings. This means that the thespian effectively performed a gross impersonation of its leader, revealed in Shang-Chi to be the hero's father, Xu Wenwu.
All Hail the King suggests that "The Mandarin," the name Killian gave to Slattery's character, was also stolen from Wenwu, but Wenwu himself dismisses this notion in Shang-Chi. Not only does he reveal the name to be Killian's invention, but he pokes fun at its true origins by remarking, "America was afraid... of an orange." In addressing this, Wenwu makes clear that despite inspiring Slattery's role, he is not and has never been the Mandarin.
That means the only one who can claim to be the true Mandarin is Killian, who declared himself as such to Tony Stark at the end of Iron Man 3. It may be Wenwu who possesses the original version's magic rings -- the namesakes of his empire in the MCU -- but Killian fulfills the Mandarin's traditional role in Marvel Comics as Iron Man's formidable foe.
There are many reasons why Shang-Chi retains Killian as the Mandarin, rather than making him Leung's character as initially announced. For one, it honors the intentions of Iron Man 3 director Shane Black. Speaking with Entertainment Weekly, he noted that Killian's dragon tattoo was meant to identify him as the MCU's Mandarin, who styles himself using Chinese imagery and terminology instead of being the "Fu Manchu stereotype" of the comics.
Ironically, the comic incarnation of Shang-Chi's father was the actual Fu Manchu created by author Sax Rohmer, renamed "Zheng Zu" after Marvel Comics lost the rights to him. Given Fu Manchu's problematic reputation and the original Mandarin's clear resemblance to him, it is understandable that Marvel Studios would reduce their influence on the villain they inspired as much as possible. By having Xu Wenwu outright mock the name, Shang-Chi cements Killian, rather than Marvel Studios itself, as having perverted Chinese culture for his own ends.
Perhaps more importantly, though, it also affirms Wenwu's arc through the film, as his late wife Ying Li (Fala Chen) always and exclusively called him by his real name. When pitching the role to Leung, director Destin Daniel Cretton consciously minimized the character's ties to the Mandarin title in favor of his tragic loss and the futile mission to reverse it. Leung then grew attached to the name "Wenwu" once it was devised, and eventually, "The Mandarin" was completely discarded as a canonical alias for his role.
Restoring Aldrich Killian as the Mandarin benefits the MCU in a number of ways. For one, it restores Black's original vision for the iconic supervillain, doubling down on Iron Man 3's controversial twist after All Hail the King seemingly retconned it to sate angry fans. But on top of that, it also allows Xu Wenwu to completely escape his controversial origins, creating a complex antagonist defined instead by his obsessive anguish which damages his family and nearly destroys the entire world.
To witness the layers of Xu Wenwu, see Shang-Chi and the Legend of the Ten Rings in theaters now.