Dane Whitman is destined to become The Black Knight, who is an Avenger. In the comics, Whitman discovers the Ebony Blade, which was forged by Merlin, and becomes the chivalrous hero. The blade is cursed and essentially is a dark variant of Excalibur. However, Whitman does lift the curse and continues his life as a hero. The Black Knight has a range of magical abilities connected to the blade when using it.
The Black Knight has a relationship with Sersi in the comics, and we see the two together in the trailer. It looks like Ikaris is going to get his heart broken. Now that's one hell of a Game of Thrones reunion.