White Skull

The White Skull (born Bucky Barnes) is the main antagonist of the Marvel comic book What If:Captain America. A Union Army officer from the American Civil War, he and his soldiers, the Redlegs Regiment, are nothing more than war criminals, murdering innocent civilians and other people of different race. His interference in a ceremony turns him into a skull-faced terrorist.

Biography
Not much is known on Colonel Bucky Barnes' early life, but at some point became a Colonel in the Union Army during the Civil War, and became the leader of the Redlegs Regiment. At first appearing charismatic, he is revealed to be a really cruel and ruthless murderer, leading his soldiers in a murderous rampage, killing villages of innocent people. When his newest recruit, Cpl. Steve Rogers refuses to partake in the murders, he shoots the kinder soldier and is scarred in the eye by a eagle. When Rogers is rescued by Union soldiers allied with Native Americans, Barnes attempt to take Rogers by force, during a ceremony to empower the dying Cpl. Rogers with ancient magic. In the process,Barnes' face is flashed by bright light that empowers Barnes too, but reflects his true self, exposing his plain white skull, as his true self is a murderer. Enraged, he orders his men to kill everyone, while he goes after an empowered Cpl. Rogers, now a superpowered soldier wielding a Native American shield that launches a magic eagle from it. After he is defeated by the new hero, redubbed Captain America, Barnes, redubbed the White Skull, rebrands his old regiment from the war as the White Skulls, a terrorist group supporting white supremacy. The fight between Captain America and the White Skull started in the Civil War is carried down by their descendants in the 21st Century.

Trivia

 * The story of What If: Captain America takes place in a alternate universe called Earth 717.
 * The White Skull is Earth 717's version of the Red Skull, the Nazi archenemy of the mainstream Captain America