I'm glad I wasn't the only one thinking that
I personally think he did it all himself, as far as any writer can. Which is to say, of course there was a bit of plagiarism or basis in real life. There always is. So yes, he did it all himself, with inspiration
I hate it every time someone says 'historical figure X was never really that good, he just got help and didn't do anything himself etc.' It's mainly people being jealous that somebody else was actually pretty good at something such as leading or creating a country. It's stupid