One of the Joker’s real names is Mr. J, and he became the Joker in a chemical accident that bleached his skin white, colored his hair green, and left him with red stains across his face.
He was originally called Jack Napier but after an incident involving a vat of chemicals which smeared clown makeup onto his face he went by many aliases including Red Hood, The Fiend with Twenty Different Faces and The Co-ed Killer. He eventually settled on the name “The Joker”. The scars are from tar washed into crevasses while he was submerged under water for long periods after an air pocket in the zeppelin bursted and it started to sink underwater.