Batman's comic debut was in Detective Comics #27 back in May 1939. It was a defining moment for the character and the start of his long and iconic journey in the comic world.
The Joker's first appearance in the Batman comics was in 1940. His origin story is complex. Some say he was a man pushed to the edge by society. He may have been a nobody, a struggling individual who then had a life - changing encounter with chemicals. This chemical exposure not only gave him his distinct appearance but also warped his mind. He developed a warped view of the world, seeing it as a place for his own brand of 'jokes' which usually involve harming others. He is an enigma, a villain that Batman constantly has to deal with, and his origin story helps to understand the nature of his evil.
The relationship is complex. Sometimes, Batman Noel urban comics might share common themes or villains with the mainstream ones, but they often explore the urban environment and its impact on Batman's adventures in a more distinct way.