And fictional… Bruce Wayne.
There’s an assumption here that our subjects would be relatively open and honest, I think.
Fulcanelli.
Acient: Jesus
Modern: Jefferson
Jesus.
Whoever was in charge building the Great Pyramid of Giza. Provided that that counts as “known to history.”
Leonardo.
Probably my great-grandmother, or perhaps great-great grand; I’d have to speak German, though.
Terry Pratchett would be good for present day.
Of course, being non-religious, I’d LOVE to have a chat with the Christ-man, if only to see if anyone would actually show up.
And then to chat about stuff, if he did.
If you did chat with Christ, would you be considered a prophet? I suppose if you asked him for some clarification on certain topics and then published the answers, that would count. You could be the first Cyber-Prophet if you posted it online.
Cleopatra, who was said to be not much of a looker but her charms was irresistable.
Plato, to talk about Atlantis, the Republic, etc.
for purely personal reasons, Frank Herbert.
if I can bring a camera along Muhammad. translator needed.
Jesus would be a close second.
Risky… Genghis Khan might not let you get a word out before your head was on a spike 
Ancient: Jesus
Recent: My mom. 
(Dec. 10, 1927 - Mar. 12, 2008)
For modern day, I’ll go with JFK. I’d like to know what his plans for his Presidency were that were cut short, and was he really shagging Marilyn Monroe?
For antiquity, I’ll go with a round table discussion with the Founding Fathers. I think that would be totally fascinating.