Harry Potter: The Worst Thing Every Order Of The Phoenix Member Did

Aberforth Dumbledore was long since a broken man. His life was never destined to be an easy one, living perpetually in the shadow of the greatest wizard of the modern age, his brother Albus sought greater purpose while Aberforth was not particularly interested in changing the world.

Disillusionment and disagreements between he, his brother, and the infamous Grindelwald lead to a duel between the three that claimed only one life: the life of the his sister, Ariana Dumbledore. Aberforth never forgave his brother for the event.

Aberforth took up running the Hogs Inn within the village of Hogsmeade and did not appear to settle for loftier goals until Harry and the resurrected Order of the Phoenix took up arms against Voldemort and the Death Eaters. Aberforth however was exceedingly late in offering assistance, as cynicism and heartbreak from the past left the younger Dumbledore with the belief that it was far too late, and did not wish to assist, thinking they were fighting a battle that was already lost.

Aberforth, to his credit, did eventually give Harry more information about the complicated history of Albus Dumbledore and offered further assistance with the final battle of Hogwarts, but one has to contemplate how much more assistance he could have provided had he taken a more proactive stance.