Dumbledore is a famous wizard who is respected throughout the wizarding world. He is the headmaster of Hogwarts school, which is something like a principal, except that the school is a boarding school where the children live during the time school is in session. Hogwarts teaches all of the young wizards how to control their magic.
Albus Dumbledore functions as one of the main role models for Harry. Sometimes his motivations are unclear, as he knows things that Harry doesn’t, and he might know things that Harry and Ron and Hermione shouldn’t know. Dumbledore was played by two different actors in the Harry Potter movies. In the first movie, the role was played by Richard Harris. Mr. Harris unfortunately died after the second movie, and he was replaced by the actor Michael Gambon, who played the role for each of the remaining six movies.
Dumbledore is portrayed as a tall man who has a long, flowing gray (or white) beard and long white hair. He is usually shown wearing a long, ornate brocade robe or sometimes more formal ceremonial robes, such as at Christmas or during formal school events.
Albus Dumbledore has a history that is portrayed as dark and mysterious, and it is not until the sixth book that author JK Rowling reveals some of his history. He had a sister who was troubled (she seems to be mentally damaged), and her death serves to convince Dumbledore that he should turn down the position of Minister of Magic (sort of like the Wizard version of Prime Minister or President), and that he should instead devote his life to recruiting and teaching students at Hogwarts.