The Ministry of Magic fears that Voldemort is killing enough people to make an army of Inferi: as they are dead, they are very difficult to stop. When Voldemort was hiding one of his Horcruxes in the past, he filled a lake in a cave with many Inferi, which were to attack and drown anyone but Voldemort who came into the cavern and took the locket. When Harry and Dumbledore took the locket, the Inferi attacked Harry; Dumbledore repelled them with a rope of fire. It is also revealed that the Inferi almost killed Kreacher after he drank from the basin to help Voldemort hide his Horcruxes, but having been ordered to return to his master after his task with Voldemort was complete, he was able to apparate out of the cave. These Inferi later killed Regulus Black when he stole the Horcrux and ordered Kreacher to destroy it.