In the creative world, there is a myth of one guy running the show.
While I think that is true in a lot of cases, there is a surprising number who quietly have someone behind the scenes. Another person or people who help them write for their public persona. Often, it is a guy who usually has a woman behind the scenes.
I will maintain a list here.
Comedy
Jerry Seinfeld very briefly said on the Marc Maron podcast that his sister helps write some of his standup.
Stewart Lee, a popular comedian in the UK also mentioned his wife helps him write as well.
Music
Mozart’s sister is believed to have written many of his early songs.
Video
George Lucas’s first wife was a world class editor for the first 3 Star Wars movies. Many people believe it was her editing that made the movies.
Science
Einstein’s first wife (another physicist) was also believed to have helped with some of his work.