It's funny how much these things are shaped by one thing. In my case it's Grandpa. I couldn't have an opportunity like this without asking him, but then I wouldn't want to have a dinner party with him and with other guests he wouldn't enjoy, so Mark Twain is much more likely to make my list than he would otherwise be.
Well, Mark Twain and Dorothy Parker for their intelligence and wit, and to see who would win their inevitable battle for conversational dominance. Cleopatra to satisfy my yearning to meet a significant historical figure, especially a woman of power. I thought about Joan of Arc but I suspect she would make an unpredictable dinner guest.