I think its difficult to guess who is most popular. There are a lot of celebrities, politicians, businessmen, etc. who are know world over but I am not sure who would be the most popular.
Maybe athletes or musicians. Like there is very few places in the world where they didn't know who is Michael Jackson is or Michael Jordan.
Your stupid question reminded me of a joke: When Abraham Liebowitz gets to school he discovers that he is the only Jewish kid in the class. But it's a decent town and nobody really bothers him. One day the teacher asks the class "Who is the most popular man in the world? and why?" And to make it interesting she held a twenty dollar bill in the air and said "whoever gives the best answer will get this twenty dollars". All of the kids called out their guesses. One said "George Washington - because he was the father of our country." "That's excellent" said the teacher. Another said "Abraham Lincoln - because he freed the slaves." "That's also good" said the teacher, reluctant to bestow an excellent, but still being polite. One little girl said "Joan of Arc - because she saved France." Another excellent choice said the teacher. Then Abraham Liebowitz, raised his hand. So the teacher called on him. "Abraham, who do you think was the most popular man in the world, and why?" And Abraham said "Jesus Christ." The teacher was shocked. "Abraham," she said "I'm very surprised. Class, I think we can all agree that Abraham should get the twenty dollars." And she handed Abraham Liebowitz the money. At recess, the teacher was still very impressed. So she asked Abraham why he said Jesus. Abraham said "Look, personally I think Moses was the most popular man in the world, but... business is business!"
I say Mahatma Gandhi, Nelson Mandela, Barack obama in politicians or leaders Titanic actress Kate Winslet and Arnold in celebrities Osama bin laden and Hitler Bill Gates...........