John Bishop was a Civil War soldier that was abducted from the battlefield by aliens. He was subjected to a series of tests (which may in part be the source of his unique abilities), and set him back down afterward. John grew to loathe aliens to an insane degree. Years later, he worked with Ulysses Simpson Grant to establish the Earth Protection Force, an agency dedicated to detecting and absolving the alien menace he perceives is coming for Earth.
Bishop is extremely long-lived and has unique fighting abilities, able to counter and take down foes that themselves are expert fighters. He also is great at improvising weapons on the spot, once using his necktie to catch an attack and even using his sunglasses as a projectile by swinging them off of his face. John is also nigh-impervious to damage and heals what injuries he does suffer very easily - he was able to survive and retreat after being impaled by a hook.
When the Turtles travel to the year 2105, they are surprised to find Bishop is the president of the Pan Galactic Alliance - essentially, the leader of the entire planet Earth, and the ambassador to other planets. It is revealed that this change in behavior toward aliens occurred when his lab caught on fire and he was pinned to the ground. One of the very aliens he hated with his every breath, that he had captured, and experimented upon, went out of his way to save John's life.