Aberforth Dumbledore was a tall, thin, grumpy-looking old man with a great deal of long grey hair and a beard (OP16). Like his famous brother Albus, he wore glasses (HBP12) and had blue eyes (DH). Aberforth was the barkeep at the Hog’s Head in Hogsmeade (EBF) and was also a member of the original Order of the Phoenix (OP9).
Aberforth, the son of Percival and Kendra, was three years younger than his brother Albus Dumbledore and one year older than their sister, Ariana (DH2, DH28). He was very close to Ariana, and after Ariana was hurt (when Aberforth would have been about seven), Aberforth shared the duty of looking after Ariana with their mother. After the dual tragedies in 1899 of the deaths of Kendra and then Ariana, Aberforth blamed Albus, going so far as to break Albus' nose at Ariana's funeral (DH18), and felt that Albus had been too focused on his personal glory to take his unglamorous responsibilities to their sister seriously enough (DH28).
He is a morally ambiguous character who hobnobs with the dodgy clientele of his pub, the Hog's Head, and indulges in illegal activities himself (HBP12).
During the 1997-1998 school year, Aberforth secretly aided Neville and several other students when they took refuge in the Room of Requirement. Later, in May of 1998, when Harry, Ron, and Hermione came into Hogsmeade trying to enter Hogwarts, Aberforth rescued them from Death Eaters, but then advised the trio that they should cut and run. Grudgingly, he helped them enter the castle and also allowed many other fighters to enter through his pub to defend Hogwarts. When the Battle of Hogwarts started in earnest, Aberforth joined the fight against the Death Eaters (DH31 ff.).
Mother: Kendra Dumbledore, accidently killed in 1899 by her 14-year-old daughter Ariana, who was mentally unstable.
Father: Percival Dumbledore, imprisoned c.1890 at Azkaban for an attack on Muggles when Albus was about 10 years old.
Siblings: Older brother Albus (born 1881) and sister Ariana (born 1884 or 1885, died 1899); both brothers are haunted by their sister's accidental death (DH3).