Michael Gambon as Dumbledore
Michael Gambon took over the role of Albus Dumbledore in Harry Potter: Prisoners of Azkaban and throughout the remaining films in the series. Ian McKellen, Gandalf in Lord of the Rings, could have easily resembled Dumbldore. But he already had a schtick with the Lord of the Rings and nobody wanted anybody getting the two series intertwined with similar old wizards with long, white beards.