Who is Alberforth Dumbledore from Harry Potter and the Deathly Hallows and what is their importance?

Alberforth Dumbledore is Professor Dumbledore's brother. He does not like or respect his brother, and he hates the way Albus keeps secrets and tells half-truths. Alberforth blames his brother for his sister's death, and he uses a fragment of broken mirror to keep an eye out for Harry and his friend. When they are locked up in the Malfoy Manor, Alberforth is watching and sends Dobby in to save them.