Dolores Umbridge - Senior Undersecretary to Cornelius Fudge, Rufus Scrimgeour and Pius Thicknesse.
The Senior Undersecretary to the Minister for Magic is a high-ranking position within the Ministry of Magic, in which is presumed to be second in command to the entire Ministry, under the Minister for Magic him/herself. Dolores Umbridge is the only person known to have held the title, serving under Cornelius Fudge, Rufus Scrimgeour, and then Pius Thicknesse, until she was arrested and imprisoned in Azkaban for her crimes against Muggle-borns.