Professor Albus Percival Wulfric Brian Dumbledore, O.M. (First Class), was a British wizard who was the Transfiguration Professor and later Headmaster of Hogwarts School of Witchcraft and Wizardry. He also served as the Chief Warlock of the Wizengamot and Supreme Mugwump of the International Confederation of Wizards. A half-blood and initially Muggle-supporting wizard, Albus was the eldest child of Percival and Kendra Dumbledore and elder brother of Aberforth and Ariana Dumbledore. His father died in Azkaban when Albus was young and his mother later died after his sister accidentally lost control of her magic, creating an explosion that killed Kendra. Albus began attending Hogwarts School of Witchcraft and Wizardry in 1892, where he would start writing with a pen-pal from Durmstrang by the name of Gellert Grindelwald.
When Albus and Gellert finally met in Britain after the latter's expulsion, Albus became entranced by the German wizard's ideas about the future of the wizarding world and how the International Statute of Secrecy is the bane of Wizardkind. The two devised a plan on starting a wizarding revolution and install a new hierarchical order led by wizards over Muggles. Albus was very instrumental to their plan; Nurmengard, the infamous dark prison that would house enemies of the revolution, was Albus' own idea. However, the two fell out when a duel instigated by Gellert and Albus' brother, Aberforth, ended up killing Ariana. Albus then broke off all ties with his friend and remained in Britain while Grindelwald sought to go through the revolution on his own. Albus meanwhile, would go on to become a wise and respected wizard within Britain and begin teaching Transfiguration at Hogwarts.
During the First World War and the implosion of Magical Europe (unknowingly orchestrated by Grindelwald), Albus remained largely out of it.