He is characterized as old, benevolent, and powerful. As such he resembles a stereotypical good wizard in the mould of Merlin or Gandalf. He is often sympathetic to Harry Potter's difficulties. He was also the only wizard that Lord Voldemort feared. Dumbledore is about 150 years old. The name Albus is from the Latin word albus ("white"), which symbolises good; "Dumbledore", which means "bee", was picked by the author because she was entertained by the concept of him strolling along Hogwarts halls and humming.
In the movie versions of Harry Potter and the Philosopher's Stone (2001) and Harry Potter and the Chamber of Secrets (2002), Dumbledore was played by Richard Harris. Harris' death meant that a replacement had to be found for the role. News reports have confirmed that in Harry Potter and the Prisoner of Azkaban (2004), Dumbledore will be played by Michael Gambon.
Albus Dumbledore has a brother called Aberforth who has been in trouble for practising inappropriate charms on a goat. Aberforth may be the bartender at the Hog's Head Inn in Hogsmeade.
When Dumbledore entered Hogwarts (about 140 years ago) he was sorted into Gryffindor. He later became the Transfiguration teacher at Hogwarts.
In the early 1940s, the Chamber of Secrets was opened. When a student named Myrtle was killed, the school was almost closed; however, Tom Riddle accused Hagrid of opening the chamber and thus caused the authorities to believe that, with the neutralisation of Hagrid, the school could remain open. Dumbledore was the only one who seemed to think Hagrid was innocent, and while Hagrid was expelled and his wand broken in two, he remained at Hogwarts as the gamekeeper.
That year a werewolf named Remus Lupin came to Hogwarts. Most headmasters would never have allowed a werewolf into Hogwarts, but Dumbledore thought that as long as special precautions were taken, there was no reason why Lupin should not attend.
The 1970s were the dark years when Voldemort was in power. Voldemort was in fact none other than Tom Riddle, who had been a student of Dumbledore years before. Dumbledore was working tirelessly against Voldemort.
In 1980, Sybill Trelawney applied to become the new divination teacher. Dumbledore hired her when she made a prediction about Voldemort. Two prominent members of the Order of the Phoenix, Lily and James Potter, knew that Voldemort was after them.
Lily and James went into hiding, using the Fidelus Charm, but were betrayed by their secret-keeper- Peter Pettigrew- and killed by Voldemort; when Voldemort turned his wand on their one-year-old son, Harry, however, the curse miraclously bounced off of him and back onto Voldemort, reducing him to a mere shadow of his former self. To keep the now orphaned Harry safe, Dumbledore placed him in the safe keeping of the Vernon and Petunia Dursley, his mother's family. This was because Dumbledore did not want the fame and being the "boy who lived" to get to Harry's head, and because the special protection that his mother had put on him was still in effect- as long as he was in a shelter where his mother's blood remained, he would be safe from any attacks (while Voldemort was no longer a threat, his death eaters were still at large, desperate and seeking revenge, as evidenced in their attacks on Frank and Alice Longbottom).
In the same year that Harry came to Hogwarts, Voldemort atempted to steal the Philosopher's stone in order to gain a new body and immortality, but failed. One year later, the Chamber of Secrets was opened again, and Harry and his friends revealed that Hagrid had not opened the Chamber of Secrets, it was Riddle himself. One year latter, the servent of Voldemort escaped, and the next year Voldemort rose again. Dumbledore re-founded the Order of the Pheonix.
Dumbledore was twice dismissed: During Harry's second year at Hogwarts, Lucius Malfoy "persuaded" the twelve governors of the school to vote for his dismissal as more and more attacks were occurring (a basilisk was petrifying people in the school). In Harry's fifth year, Harry and some more students organised a club called "Dumbledore's Army". When Dolores Umbridge discovered it, she managed to contact the ministry and they sacked him.
In that same year, the Ministry of Magic refused to believe that Voldemort was responsible, and orchestrated a smear campaign against Harry Potter. The campaign had partial success, convincing a part of the population that Harry was indeed an attention-seeking lunatic and making his life miserable, but ultimately failed when Voldemort himself was seen in the Minstry of Magic by numerous eye-witnesses. Cornelius Fudge was forced to accept that Voldemort had returned and the media followed suit, being sympathetic to Harry again to fit the new situation and public opinion.
See also: Harry Potter and the Philosopher's Stone