When talking about famous people it is customary to call the by their last name, but when talking about a famous French emperor and military leader, most people use his first name. Is this something that only happened after his death or was it always true?
I've wondered this as well! My best explanation is that he became Emperor of France, and we tend to refer to monarchs by their first names (Elizabeth I and not "Tudor").
EDIT: I found a previous thread with the exact same question, plus answers: http://www.reddit.com/r/AskHistorians/comments/1n8pms/why_is_napoleon_known_as_napoleon_and_not/
He was Emperor Napoleon I. His nephew was Napoleon III. There might be other reasons, but its also a royal name like King George III or Queen Elizabeth II.
He IS referred to as Bonaparte. That is, when he is spoken of in France regarding the time before he became emperor, he's referred to as Bonaparte, which was his name at the time. If talking about him after he became Emperor Napoleon I, then he's referred to as Napoleon. It's simply using the correct name to refer to him given the context. Royalty typically are not referred to using a last name. We say King Louis XVI most typically. But when he was on trial during the French revolution, they called him in court "Louis Capet", which was technically his full name, without title. On the other hand, in English, he's typically referred to as Napoleon all the time, whether talking about him before he became emperor or after he became emperor. There's not so much concern about the appropriate niceties about what he was called during which time period. It's just the historical convention--he was primarily known as "Napoleon" during his lifetime in England so the name has continued. But in France, where he's a much more integral figure in their history, they tend to distinguish more what they should call him at each time period.
It depends of what period of Napoleon's life you are talking about. For exemple, when he is a general, we say "Le général Bonaparte". Napoleon is his name as Emperor, so the most widely used.
The same thing his true for Napoleon III : When he is President, we say "Prince-Président Louis Napoléon Bonaparte", and when he is Emperor, "Napoléon III"
Thanks for all your comments! Apparently the reddit search engine doesn't like me. I tried searching before posting but I didn't find anything. Oh well.