Obliviate

Obliviate is one of the most quietly important charms in the wizarding world. Cast on a target, it removes specific memories — events, conversations, faces, entire periods of life — and seals the gap so cleanly that the target never realizes anything has been taken. The Ministry of Magic's Obliviator Headquarters maintains an entire department of trained witches and wizards who do nothing but Obliviate muggles after every accidental magical exposure: a witch's broom seen through a window, a wizarding duel overheard at a party, a magical creature spotted in the woods. The charm is the wall that keeps the wizarding world hidden.

The classic literary case study in Obliviate's danger is Gilderoy Lockhart, the celebrated author and famously fraudulent Defence Against the Dark Arts professor of Harry's second year. Lockhart's entire career was built on Obliviating actual heroes after they shared their adventures with him, then publishing the stories under his own name. When he tries to Obliviate Harry and Ron in the Chamber of Secrets using Ron's broken wand, the spell backfires onto himself and erases Lockhart's entire memory — name, identity, family, everything. He spends the rest of the series in St. Mungo's, mostly happy, with no idea he was ever anyone in particular.

Hermione casts the most quietly devastating Obliviate of the entire series in the opening of Deathly Hallows. Knowing her parents will be among the first targets if Voldemort's Death Eaters trace her family, she modifies their memories so completely that they no longer know they have a daughter named Hermione, and gives them new identities as Wendell and Monica Wilkins, sending them to live in Australia with no memory of magic, of England, or of her. She tells almost no one. The intent is to bring them back when the war ends, with the charm reversed; the book leaves whether that fully succeeds slightly ambiguous.

Reversing Obliviate is genuinely difficult. Specialized healers can sometimes recover the lost memories, particularly if the cast was sloppy or partial; a clean professional Obliviate is, for most practical purposes, permanent. The Ministry treats unauthorized Memory Charms on witnesses as serious crimes — though, given the Ministry itself authorizes hundreds per year on muggle witnesses, the line between official and unofficial is sometimes uncomfortable.