Ben Kingsley was instrumental in creating his character Trevor Slattery's dressing room in 'Shang-Chi'

• Sir Ben Kingsley makes an MCU come back in "Shang-Chi" as the actor Trevor Slattery.
• Trevor is living in Wenwu's compound as his jester, putting on one-man Shakespeare plays.
• Production designer Sue Chan said that Kingsley had "very clear" ideas about Trevor's dressing room.

Sir Ben Kingsley's return to the MCU as Trevor Slattery in "Shang-Chi and the Legend of the Ten Rings" took many by surprise, but it turned out to be a stroke of ret-conning genius on Marvel's part.

We re-meet British actor Trevor Slattery when Shang-Chi (Simu Liu), along with Xialing (Meng'er Zhang), and Katy (Awkwafina), stumble across him in Wenwu's compound.

Trevor is living in a prison-come-dressing room, and explains that he's basically existing as Wenwu's (Tony Leung) jester, performing Shakespeare on a weekly basis for him and his cronies.

Speaking to Insider, production designer Sue Chan said that Kingsley helped to create this prison-dressing room. In fact, he was incredibly involved in the process of bringing the set to life.

"Sir Ben was terrific. He had a very clear cut idea about how Trevor Slattery would live there," Chan said. "Trevor's character is a prisoner, of course, of Wenwu, but he kind of holds a special place there. He's still there first of all, and he is a working actor so you really wanted it to feel like he is using that space to deepen his understanding of characters like King Lear."

"Sir Ben really wanted a particular volume of Shakespeare that Trevor Slattery would have had that he would have requested from Wenwu," she continued, adding that they "found" the book to make his dressing room complete.

In the MCU, Slattery is a British actor who was hired to portray a terrorist called the Mandarin in "Iron Man 3." This persona turned out to be a front for Guy Pearce's Aldrich Killian, who styled himself as the real Mandarin. Neither versions were actually the real person, however, and while Killian died, Slattery was broken out of prison by the Ten Rings and taken to Wenwu's compound.

There, Slattery saved himself from his own execution by bursting into a Shakespeare performance. The Ten Rings loved it so much, he's lived there ever since as a "working actor."

It's clear by the set details that Slattery considers himself a true thespian, too.

"Trevor's a bit of a narcissist, so we had a poster of Trevor Slattery's King Lear back when he did it in that fictitious theater in some part of London. We made a fake poster of that and we stuck that up there," Chan said. "And then he is a football fan and so you might notice the Liverpool scarf and all of that."

Chan noted that "there were just a few elements that Sir Ben insisted on having ... he just really wanted the focus to be on his dressing room table."

On Trevor's dressing room table lies the aformentioned volume of Shakespeare, plus a wig on a mannequin's head - while the grand mirror surrounding by dazzling lights grabs the majority of your attention.

It's unclear what Kingsley's MCU future may look like, if indeed he has one. Still, it was a welcome return for Slattery, who helped to fix the MCU's troubled history with the Mandarin and finally present to us the true version of the character.

"Shang-Chi and the Legend of the Ten Rings" is in theaters now.