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

Mundungus Fletcher was an unliked, but necessary part of the Order of the Phoenix. A thief and a scoundrel, Fletcher made his living dealing in the acquisition and sale of magical artifacts. At some point in his history, Dumbledore had aided Fletcher, earning a fierce loyalty. This proved a prudent move, as Mundungus utilized various contacts in the seedier parts of the wizarding world to act as a spy for the order.

Mundungus never quite shook his habit of looking out for himself exclusively, however. Shortly after Sirius Black's death, Fletcher was discovered to have been stealing things from the headquarters of the Order, an establishment now belonging to Harry, in order to sell them. Among these included one of the fabled Horcruxes, which he then was coerced into giving to Dolores Umbridge.

Perhaps worse than that, Mundungus was a member of the guards who transformed to look like Harry upon his escape from Privet Drive. However, as soon as a cavalcade of Death Eaters and Voldemort himself appeared, Fletcher's true nature reared its ugly head, and he disappeared from the fight, leaving his charge unguarded.

Mundungus is a classic example of a bad guy fighting for the right cause. He has good qualities to him, just don't expect him to do anything unless a debt is held over his head.