Well, I'd like to be able to meet Thomas Jefferson and spend an evening over dinner and cigars ... one of the founding fathers, author of the Declaration, the president who began the expansion of the US in a big-time way, inventor, gourmand and highly noted conversationalist ... in fact, his inventions of the dumb-waiter and the lazy-susan were an outgrowth of his desire to have the conversation uninterupted at the dinner parties he hosted ... wine was brought from the basement and the door from the kitchen to the dining room became the lazy susan, and he served his guests personally ... he was a leading foodie of his time and began using the tomato at a time most in this country believed it to be poisonous ...
Fictional character ... Sherlock Holmes. One of the most renowned minds of all time, a brilliant thinker and, when in the right mood, a fascinating conversationalist.
I liked JRs idea of more than one ... a dinner party, if you will. First among the real people I'd add to the list would be William Bligh (Captain of HMS Bounty, he took a group of men in f-ing row boats (!) through open seas greater in width than the US and got them home to England. "Men Against The Sea" is a story of overcoming long odds equalled by few others (Apollo 13 among the equals).
Second among real people would be Douglas MacArthur. Among the most scholarly and well read of all military people, brilliant mind and one of the best military tacticians of all time. His strategies in WWII saved the lives of millions of Americans, then his stewardship of Japan paved the way for their emergence as a major player in the modern world.
Among fictional characters I think would be fun to add would be Captain Nemo (20,000 Leagues Under The Sea) for reasons that are obvious to readers of Jules Verne's book) and Tom Sawyer (for reasons much like those mentioned above for his friend Huck, but also because he was an original thinker who in adulthood could have become a truly world-class leader of men).