Ministry: Minister of Magic
Thicknesse becomes the Minister of Magic after the death of Rufus Scrimgeour. Unfortunately, Thicknesse is literally Voldemort's puppet – during his entire time as Minister, he's under a Death Eater's Imperius curse. Great.
As a result, the Ministry begins to persecute Muggle-born wizards and, in fact, any wizards that can't prove they're from pureblood wizard families. When he fights alongside the Death Eaters in the Battle of Hogwarts, Percy hits him with a jinx.