Clea is an extradimensional energy being from the Dark Dimension who becomes fascinated with Doctor Strange, and after an apprenticeship-turned-relationship between the two, they actually get married(ish). When Strange dies in the comics, she even ends up taking over as the Sorcerer Supreme. Oh, and as it happens, she's also the niece of Doctor Strange's most dangerous enemies, Dormammu — yep, the villainous entity from the first "Doctor Strange" movie.
The whole thing is precisely as convoluted as you'd expect from a juicy comic book plot that's been running on and off since Clea's debut in 1964. Her power levels, too, have fluctuated wildly over the years, from virtually powerless to a borderline Dormammu-level threat. However, because she's trained by Stephen Strange, she has fairly similar magical abilities as he does, as reflected by her own Sorcerer Supreme status later in the game. In addition to this, Clea a Faltinian, which means that like her uncle Dormammu and her mother, Umar, she's essentially comprised of magical energy — which gives her far more strength, resilience, and magical punch than your average human can hope to have. She's also far, far older than her youthful appearance would suggest.
Clea is a fairly prominent figure in Doctor Strange's comic book adventures, and despite the fact that the MCU Strange focuses every drop of his romantic affection on Christine Palmer (Rachel McAdams), it's not exactly a surprise that Clea's name has been popping up as of late. After all, it's a mad old multiverse, and all sorts of folks might turn up.
"Doctor Strange in the Multiverse of Madness" premieres in theaters on May 6.
