re: who is considered the greatest/biggest movie star of all time?

The correct answer IMHO is John Wayne. The man made movies from the mid 20's to the mid 70's and his fame and appeal never diminished. Today we buy movie tickets based on the storyline and the film's perceived ability to entertain us. Few of us fork over our cash just to see a certain actor. However, that was the case with John Wayne. If he was in it then storyline didn't matter. It was simply a John Wayne movie and that alone is what brought people to the theater.