I want to write a novel where the main character is a real person, someone famous. What are the steps to ask permission to do so? Who do I have to contact? (like the person's agent, lawyer, etc.)
Start with your IP lawyer and make sure you do everything required the correct way.
But why? What will you do when they say no? Why should they say yes when they have no idea how your novel will actually portray them?
If it is an incidental use you may not need permission. You need to start with your IP lawyer.