A man named William survived the destruction of Kansas. He saw Superman as a savior of humankind and created a church worshipping him. Superman tried telling William he wasn't a godly being.
William was later given powers that drove him insane. Calling himself Gog, he vowed to kill Superman. With the death not satisfying enough, Gog went back in time and killed Superman over and over, each time with a different method.
With the arrival of the Kingdom Come Superman in the current timeline, what may be a coincidence has occurred. Former FBI agent, Mr. America discovered that a couple of metahuman criminals that claimed to be Demigods were found dead with holes blown through their chests. He then finds several more "Demigods" dead, the New Olympians. Watching from behind stood a man in the shadows with horns on his head. Carved at the scene was the word, "Gog."
Mr. America, badly beaten and barely able to walk, staggers into the Justice Society Of America headquarters and asks if they've ever heard of "Gog."
After Mr. America is treated and Kal, the Superman from the future (Kingdom Come Superman) tells them about Magog from his world, Mr. Terrific tells them that Gog was a normal man born in Chicago. He was a missionary in Africa and then disappeared. When he returned, he was wearing the armor and had the staff. He called himself Gog and attacked Superman.
Kal goes to Metropolis to ask Superman why Gog attacked him. Superman tells Kal that Gog just appeared and attacked him. He claimed to be from the future and was the only survivor of a nuclear explosion in Kansas that he failed to prevent. When Superman had Batman look into Gog's background, Batman discovered his real identity. They figured he was just disturbed. Kal tells him that maybe Gog was able to somehow catch a glimpse into future. He tells Superman about the destruction of Kansas in his time and how his wife, Lois, was killed by the Joker. He arrested the Joker and before his trial, a man calling himself Magog killed him. Soon the people treated Magog as a celebrity.
Their talk is cut short when Kal hears someone calling themselves a God in Gotham. They both fly there to find Hercules getting beat by Gog. After dealing with an angry Hercules, they enter the museum just in time to witness Gog teleporting away. In the Congo, Gog walks down some ancient stairs carved into a mountain saying he will get rid of the gods that walk the world for they will not save them. He will make the way for the only savior that will do the job. He then kneels before a giant head carved or trapped in the side of the mountain.
It is unclear whether or not Gog is, in fact, Magog.