A question about Harry Potter?

Did Dumbledore actually do anything of value during the entire HP series? Harry Potter does nothing but praise him and refer to him as "the greatest wizard of all time", but the reality is that he is a terrible headmaster putting his students in danger and conveniently going off to do some official work while his students are in danger (like when the Sorcerers stone was in danger of being nabbed) and conveniently shows up after the danger is all over with. The only time he actually tries to do anything magical first hand (yes he did send a Phoenix in the chamber of secrets but it seems he could have also gone there himself and done something rather then doing so himself he risks the life of a 12-13 year old Harry Potter) he gets himself killed.