25Worthless: Lucius Malfoy
Despite being one of Voldemort's most important Death Eaters, Lucius Malfoy had a knack for messing things up for the Dark Lord. When Lucius believed Voldemort was gone forever, he tried to rid himself of the diary Voldemort entrusted to him for safekeeping many years ago. In doing so, Lucius
put the diary on a path where it would eventually be destroyed by Harry Potter himself.
Lucius's actions led to one of Voldemort's Horcruxes being destroyed, which in the long run made Voldemort more vulnerable. Lucius was also tasked by Voldemort to lead the mission to the Department of Mysteries in Order of the Phoenix, in which he failed to secure the prophecy, not to mention got himself and many Death Eaters arrested and taken to Azkaban.