The Green Knight
John Bernlad. Billionaire, playboy, philanthropist. Tech wizard. CEO of Bernlad Heavy Industries.
Everyone knew his name. Some wanted to be with him, some wanted to be him. He grew up rich, privileged, brilliant. He had every advantage. He coasted through school, barely trying. He made his already successful company even more successful with a number of patents and inventions, most of which were in military and defense applications.
Then, his estranged and eccentric great-great uncle finally died of old age. John was his only heir. The single bequest arrived in a very old but solid great just a few days later.
Inside the crate, packed in brown paper and straw, was a truly ancient mail shirt, like the ones worn by the Celts and Anglo-Saxons of Britain in the 5th century. Along with it, an equally ancient helm and axe. The most odd thing about them, other than the complete lack of any rust or decay, was their dark green color. They seemed , perhaps, to have been lacquered. A note lay under them in the box. "This is the armor of the Green Knight. Whilst you wear it, no lasting harm may befall you."
John didn't really believe it, but he tried on the armor at a whim, and discovered that it filled his body with a rush of power. Wearing it, he was nearly invulnerable, would heal from any wound he did take, and his strength was greatly increased. Something about the armor wakened childhood dreams of chivalry and heroism, and he resolved to use the armor to fight evil.
He has done so ever since, and was a founding member of the Vanguard.
The Green Knight does keep secret the mystic nature of his armor. Using his technical skills and vast fortune, he has enhanced the armor in many ways, and concealed the magical chain shirt beneath layers of modern hyper-alloy plate. He portrays himself, and his armor, as a technological marvel, rather than an artifact of Arthurian times.