It could be a number of authors. Some well-known detective creators include Arthur Conan Doyle and Agatha Christie, but there are many others depending on the specific detective you have in mind.
One famous fictional detective is Hercule Poirot. He's known for his meticulous attention to detail and unique approach to solving crimes. His cases often involve complex plots and surprising twists.
One possible fictional detective who was a janitor is in the mystery series 'The Unsung Sleuth'. In this story, the main character, Detective Mark, starts off as a janitor before solving complex cases.
I'd say Hercule Poirot is pretty famous. His unique methods and meticulous approach to solving crimes have captured the imagination of many. Also, his character has been featured in numerous books and adaptations.