Here's the story behind Superman's bizarre doppelganger Milkman Man, who first appeared in JLA/Doom Patrol Special #1. There has been any number of alternate versions of Superman since his first appearance. This includes the famous "Reign of the Supermen!" comic arc, which followed on from Superman's death at the hands of Doomsday. This saw the rise of a number of potential replacements for the Man Of Steel, including Cyborg Superman and the Eradicator.
Another popular alternate take from the comics is the Elseworlds story Superman: Red Son, which explores what would have happened if he was raised in the USSR instead of America. The live-action movie versions of the character haven't really dived into this aspect, however. Superman III saw the character becoming a darker version of himself, ending with the corrupted Superman splitting in two and fighting Clark Kent. Superman IV: The Quest For Peace originally featured a Nuclear Man prototype that bore a resemblance to Superman's copy Bizarro, though this villain was later cut from the movie. Justice League also briefly featured Henry Cavill's Superman going rogue following his resurrection, though he quickly snaps out of it.
Easily one of the oddest alternate versions of Superman is Milkman Man, who debuted in JLA/Doom Patrol Special #1. This comic is part of the "Milk Wars" crossover event, where DC's biggest heroes meet with characters from the Young Animal imprint. Other comics from this arc include the Mother Panic/Batman Special and Cave Carson Has A Cybernetic Eye/Swamp Thing Special. The story of his comic revolves around a corporation called Retconn, who have the power to alter entire realities to make them more marketing friendly. The Doom Patrol arrives in a place called Happy Harbor, which resembles a quaint little American town from the 1950s.
This reality also contains Milkman Man, a version of Superman who - like the name suggests - dispenses milk to the neighborhood and makes sure the residents are happy. The Justice League of this reality has also been twisted into the Community League of Rhode Island, who have been corrupted after drinking the milk of psychic cows. The story reveals this version of Superman is actually the child of Terry None and Casey Brinke, who was later adopted by Retconn to become their weapon.
Trying to fully map out the plot of the JLA/Doom Patrol Special is a little tricky since it gets pretty insane, but it essentially ends with Retconn hitting the Final Refresh Button, which will wipe out all of existence. The team manages to prevent this, though Milkman Man is wiped out in the process. The "Milk Wars" storyline was appropriately bizarre and hilarious, with Milkman Man being a fun skewing of Superman's wholesome image.