Aberforth Dumbledore was one of the most overlooked characters in the entire Harry Potter series. Even his own brother managed to forget he existed most of the time. The most Albus ever told Harry about his brother was that he had an unnatural interest in goats, but never (thankfully) elaborated. Harry had to find out from Rita Skeeter’s awful book about Albus that Aberforth is the one who broke his brother’s nose for the first time, and the reason why he did it. Harry also found out from the book that Albus and Gellert Grindlewald had been friends at one time…but that’s another post.
Aberforth, for all his talk about giving up when Voldemort was trying to take over, did just as much for the light side as his brother had ever done, if not more. He hid Harry and his friends from the Death Eaters, he helped Neville and the other students by supplying them with food and anything else they needed after they started hiding out in the Room of Requirement (all without the Death Eaters finding out what he was up to), and he sent word to the rest of the Order to come to Hogwarts for the final battle and let them all go through his pub to get to the school once they arrived. He managed to do all this right under the Death Eaters’ noses, openly defying them every chance he got, knowing that they didn’t dare touch him because they needed him. He appeared to be playing both sides, at best he appeared to be a neutral party, when in reality everything he did was for the sole purpose of helping the Order in their fight against Voldemort…okay, and also trying to stay alive long enough to hopefully see the end of Voldemort once and for all.