Which 'Godfather' character is the most popular?

Don Vito, of course.

Marlon Brando

It has been argued that Marlon Brando's portrayal of Vito Corleone was the role of his lifetime, the one he was "born to play." Similar matchups include George C. Scott as "Patton," Raymond Burr as "Perry Mason," and Robert Duvall as Gus in "Lonesome Dove." In cases like these, other actors who play the same parts in sequels or revivals are often rejected as being "off" or "wrong" or "not believable." It is interesting that Brando was cast as Corleone over the objections of Paramount Pictures executives, who preferred Ernest Borgnine, and even suggested Danny Thomas as the Don. Brando won an Academy Award for Best Actor for his work; being Brando, he refused to accept the Oscar.