Well, Fatman isn't based on a true story. It's a work of imagination, crafted to engage and thrill the audience without drawing from actual events or individuals.
I'm not sure which specific 'Fatman' real story you are referring to. There could be many things named Fatman. It could be a nickname for a person, or perhaps related to a specific event, product or even a fictional character in a certain local context. More details would be needed to accurately tell the story.
If 'Fatman' is a person, the main aspects could be his personality. For instance, if he was a jovial fat man, his relationships with others in the community would be a main aspect. Maybe he was always the life of the party, or perhaps he was a bit of an outcast at first but then won people over with his charm. His daily life, like what he did for a living, would also be part of the story.
I haven't come across any reports stating that Jake Tapper is penning a novel. His focus seems to be on his journalistic endeavors, such as reporting the news, conducting interviews, and providing analysis. However, it's not impossible for him to venture into novel - writing in the future, but for now, there's no indication of it.