Dumbledore's Army
Aberforth allows the resistance fighters to use a secure passageway from the Hog's Head to the Room of Requirement through Ariana's portrait, it being the only unguarded entrance into Hogwarts. This passage is used to evacuate underage students from Hogwarts and, according to Neville, it was also used by members of Dumbledore's Army to get food when they were living in the Room of Requirement because that is one thing the Room of Requirement would not do. Aberforth leaves the Order, believing the war against Voldemort is lost. However, he quickly joins the Battle of Hogwarts and is last seen Stunning Augustus Rookwood. According to Rowling, Aberforth survives the battle, and is still "at the Hog's Head, playing with his goats".