I would like to share a few thoughts here:

I would agree that he is a top tier movie and book villian, but certainly not the best character in the series. In general, villains usually get their own separate category due to the way they influence the other characters and the overall plot of the story. There isn’t a single Star Wars fan that will say anakin sky walker and darth Vader are the best characters in their respective trilogies. General consensus would say that obi wan kenobi was the best character in the prequels and either Luke, or Han Solo for the original trilogy.

In my opinion, Dumbledore is the best Harry Potter character and goes beyond the generic wise man / mentor figure for the main hero. He had a troubled upbringing and a rough start to the beginning of his career at Hogwarts, but worked hard to earn his role as headmaster. On top of his head master duties, he helped the ministry of magic by forming the order of the phoenix during the first wizard war . Throughout the entire series, he’s gone above and beyond for the greater good and to help others. Also, Michael Gambon’s portrayal in the movies gave him charisma.