Prester John, or Johann as his real name is, was a time-traveling villain whom met and fought with the Fantastic Four on one occasion. He dressed and spoke as they did in the Middle Ages and had a few more run-ins with other heroes such as Iron Man and Thor.
Later on, the warrior rethought his ways and instead of being a villain, he wanted to become a force of good.
Prester John was created by Stan Lee and Jack Kirby and first appeared in Fantastic Four Vol.1 issue 54 (1966).
Major Story Arcs
Cable and Providence
He got his opportunity when the X-man Cable invited him to join him on his own private island known as Providence, on witch Cable wanted to start a new community and a new way of life. John happily accepted and became the director of security. A job he very much liked an did well. However, even John's tight security could not help an invasion of Mr. Sinisters' Marauders. Their mission was to take down Cable, and nearly succeeded. Although Cable survived, the island nation of Providence was destroyed beyond repair. Prester John accompanied his fellow citizens back to the American coast, but just like the island he had protected, his dream was destroyed.
Against the Defenders
Not much was heard from Prester John again until he clashed with a superhero team known as the Defenders. While the team of Defenders had crashed into the mountains wile investigating some strange occult happenings, John, apparently back to his old villainous ways, shot Iron Fist from short range. Why did this, remains to be seen as of now.
Prester John has no superhuman abilities. He excels at use with most crusade age weapons and is gifted with exceptional strength and agility. He often used a mace-type object he deemed the Evil Eye.
It was able to project bolts of concussive energy as well as be used as a melee weapon. It also had the special ability to create and destroy force fields.