David Graves was a prominent author who wrote books about many of the world's mysteries, including such topics as the lost city of Atlantis, the Bermuda Triangle, Stonehenge and the Belmez Faces. When he and his family was saved from Darkseid by the group of super heroes who would soon form the Justice League, he wrote his most popular title, Justice League: Gods Among Men.
But his family grew ill killing off his wife and two kids. He too started to get sick, he blamed the Justice League for being exposed by something unknown when Darkseid attacked. So he travels to Mount Sumeru, to find the "Valley of souls". To try and bring his family back.
David Graves was created by Justice League writer Geoff Johns and artist Jim Lee. Johns described Graves as a character who would take the classical monomyth or "hero's journey" narrative device, and turn it on it's head, illustrating how a villain would go through a twisted version of it, becoming a major threat for the Justice League.
Major Story Arcs
In The New 52's origin of the Justice League, David Graves, his wife Jennifer, and his two children, Jason and Emma, come under attack by Darkseid's forces. Accepting what he believed to be his fate, and covering his children's eyes for their inevitable death, Graves and his family are saved by the superheroes that would eventually become the Justice League. After these events, Graves is inspired by the events to write a book about the team called Justice League: Gods Among Men.
The Villain's Journey
A year after Grave's book about the Justice League, an unknown event had caused him to fall terminally ill, with his family no where to be found. His doctor suggests he try to contact the Justice League, as if they knew why he was suffering, they'd surely help, but Graves declines, no longer feeling that the League were "gods." The doctor informs Graves that putting him through more chemo or other treatments would be pointless. With the prognosis, Graves says "then my journey must begin" as he shoots and kills his doctor.
Four years later, Graves reappears, having gone through a drastic transformation, physically unrecognizable to his former self, with the faces of Jason and Emma, his son and daughter on his inner forearm. Graves infiltrates Argus's secret storage facility known as The Black Room, where they keep the world's most powerful mystical items, stealing the Orb of Ra. Later, writing a personal manifesto, he notes that the way to destroy the Justice League would be through their public liaison Steve Trevor, who he mails a copy of his Justice League book.
Graves would then begin interrogating some of the League's enemies, like The Key and Weapons Master, in order to discover their weakness. His final target would be Steve Trevor, who he abducted and tortured. Graves got Trevor to break by threatening to kill his sister and her child in front of him. He got into the Justice League's Watchtower where he attacked them before abruptly leaving and going to Tracy Trevor's house. When fighting started between the members of the Justice League, he somehow managed to broadcast the combat all over the world. When they follow him to the Valley of Souls, it appears that he had already killed Steve Trevor who seems like he is still to play a part in his plans.
Little is explained about his powers at the time. But it explains that he uses spirits to feed off of people's misery. Which has shown to be able to take on the Justice League.
His transformation seemed to make him a bridge between life and death and gave him control of Pretas, spiritual parasites with taste for human misery. The Pretas seem to feed by phasing through their prey and making them experience their saddest memories in the process, this ability works even on metahumans of Superman's caliber. They are also able if turning themselves into mirages of deceased beings (like Batman's parents or GL's father). But they are also able to bring out what their prey thinks it's biggest misery is, for example: Cyborg was conflicted about what he became after the accident and the spirits showed him his human self (which he thought has died) or Wonder Woman seen Steve Trevor because she thought he has died (and also had not experienced other 'human' loss in her life).
Otherwise he is superhumanly strong and tough and is able to fight Justice League on his own. The relation between his physical attributes and the misery his Pretas feed on has not been specified yet.
He is an accomplished novelist and has self-taught understanding of human psychology.