Madam Rosmerta

Madam Rosmerta is the landlady of The Three Broomsticks pub. She is described in the books as "a curvy sort of woman"; several pupils, including Ron Weasley, therefore have a crush on her. In Prisoner of Azkaban, Madam Rosmerta is angered when Dementors were in Hogsmeade because their presence is scaring away many of her customers. Apart from hosting an informal meeting between McGonagall, Cornelius Fudge, Filius Flitwick, and Hagrid, and being the object of Ron's infatuation, she does not play a major role in the early part of the Harry Potter series.
In Half-Blood Prince, however, it emerges that Rosmerta has become an unwitting agent of the Death Eaters. In order to fulfill his mission to assassinate Dumbledore, Draco Malfoy had managed to place Rosmerta under the Imperius Curse. He used her to pass on a cursed necklace to Hogwarts student Katie Bell, who accidentally touched the necklace and was herself subjected to the very harmful curse intended for the Headmaster. He also commanded her to send a bottle of poisoned mead to Horace Slughorn intending it to be a Christmas present for Dumbledore after overhearing Hermione mentioning that the security on the school wouldn't recognise something put in the wrong bottle and knowing that a package from Rosmerta would not be checked. Malfoy communicated with Rosmerta through fake Galleons. After Harry and Dumbledore had been to the cave to retrieve a locket they believed to be one of Voldemort's Horcruxes, they Apparated to Hogsmeade, where Madam Rosmerta alerted them to the presence of the Dark Mark above the school and gave them brooms on which they could travel rapidly back to Hogwarts, where Draco's plan could be brought to completion. Rosmerta was among those paying respects at Dumbledore's funeral.