The MCU's next superhero, Sir Percy of Scandia. The MCU version of the Black Knight will be played by Kit Harington, and his precise role in Eternals is unclear.
The Black Knight is an unlikely addition to the MCU. He's not exactly an A-list superhero; although he was an Avenger for a time, that was a period where the Avengers were second- (or probably third-) stringers in sales next to the X-Men and Spider-Man. The rest of the Avengers have historically treated the Black Knight with a degree of disdain, disturbed by his habit of narrating to himself in a fake Olde English accent as a coping mechanism to attempt to rein in the Ebony Blade's dark influence. Yet, for all that's the case, recent comics have retconned that the Black Knight is actually more powerful than Thor himself.
Thor may have Ebony Blade is the antithesis to Mjolnir, in that it "lightens only in shadow." The more unworthy the person who wields the Ebony Blade, the more powerful it becomes. When Dane Whitman meditates upon his own inner darkness, his wounded pride and vanity, the Ebony Blade becomes a WMD.
The striking thing is that this makes the Black Knight more powerful than Thor himself. Black Knight: Curse of the Ebony Blade #3 featured a flashback to the days of ancient Camelot, when Thor Odinson led a group of Viking raiders in an attack upon the city. Black Knight stood in its defense, and Thor couldn't resist taunting him as he battled Arthur's champion. He had no way of knowing that Black Knight became ever more powerful as Thor undermined his confidence and fueled his self-hatred until finally, the Ebony Blade erupted in a flare of cosmic power. One blast was enough to knock the Odinson out. Ironically, Thor can count himself lucky he wasn't killed; the Ebony Blade consumes the souls of its victims, so this could have been the end of the Thunder God.
This is how powerful Black Knight truly is in the comics, and it will be fascinating to see how he is handled in the MCU. All these retcons have been brought into place over the last year, since Marvel Studios president Kevin Feige was appointed Chief Creative Officer of Marvel Entertainment, giving him creative oversight over the comics. That means it's entirely possible Black Knight's powers have been amplified in the comics ahead of Eternals - in which case, Dane Whitman could be one of the MCU's greatest powerhouses to date, easily suring Thor.
