This is my very own interpretation of the DC Comics Universe, character-by-character.
Justice League[]
Current Roster
Around the beginning of the Age of Super-Humans, a being known as Starro the Conqueror and his army of starfish-like aliens attacked Earth with the intention of taking control of it.
However, a collective of heroes, led by Batman and Martian Manhunter, fought the invasion and, despite some fiction between the group, managed to overthrough the invaders. They then decided to stay together as a way to protect Earth from similar threats.
The League's roster has both expanded and decreased over the years, but the team's heart and soul really seem to be the "Holy Trinity" of the group: Superman, Batman, and Wonder Woman.
Founding Members - Batman (Bruce Wayne); Superman (Clark Kent); Wonder Woman (Diana of Themyscira); Green Lantern (Hal Jordan) (Resigned); The Flash (Barry Allen); Aquaman (Arthur Curry); Martian Manhunter (J'onn J'onzz)
Later Recruits - Hawkgirl (Shayera Hol); Green Lantern (John Stewart); Cyborg (Victor Stone) (Co-Leader of the Teen Titans); Nightwing (Dick Grayson)
Martian Manhunter[]
Green Martian J'onn J'onzz lived a peaceful life of Mars with a wife and child. However, this all came to an end when the antagonistic White Martians, who lived on the other side of the planet, took over and completely wiped out all the Green Martians. Near the end of the battle, J'onzz witnessed the execution of his family before unexpectedly teleporting away.
He soon found himself on Earth, and discovered the reason for his transportation of an experiment by a scientist who, upon seeing him, died of a heart attack. Seeing no reason to return home, J'onn managed to adjust to life on Earth, creating a new persona as "John Jones", a homicide detective for the Gotham City Police Department, where he often encountered the vigilante Batman.
Becoming his partner within the system, Batman and J'onn became partners and soon discovered a planned invasion of Earth by Starro the Conqueror. Gathering up some of the world's most powerful beings, they become founding members of The Justice League and defeat Starro. During this time, J'onn takes up a new appearance, a Martian-Human Hybrid, and becomes a full-time member of the League, thus ending his partnership with Batman, who chose to remain in Gotham as a part-timer.
Powers and Abilities - Superhuman Strength; Shapeshifting; Genius-level Intellect; Master Detective