Although it is unknown who invented it (the spell was created in Africa) it was brought to Britain and hence to the world in the 17th century by Eldon Elsrickle. He used it to terrorise London, stealing from homes of Muggles and wizards alike, until Blagdon Blay invented the Anti-Alohomora Charm.
Before Alohomora, the most popular unlocking spell was Portaberto (used to splinter a lock from a door; though known to occasionally leave a smoking hole where the key should have gone) and, before that, Open Sesame (which ripped doors from their hinges and tore them into firewood). All of these were more rudimentary and by far less subtle than Alohomora.
Descriptions of this spell are written in numerous books, including the first volume of the Standard Book of Spells series, where it is described in chapter seven and a spellbook that can be found in the Hogwarts Library. This spell is also taught in Charms class to first years at Hogwarts school of Witchcraft and Wizardryand is one of the first spells students learn.
There is a spell called the Anti-Alohomora Charm which is used to counteract this spell. Magical locks also existed and were placed on several doors, but could be unlocked with this charm.
|Eldon Elsrickle||1600s||The first wizard to use it in the western world. Elsrickle had learnt the spell from an Ancient African sorcerer and used it to ransack the houses of London, Muggle, and wizarding alike.|
|Newt Scamander||6 December 1926||Opened a safe at Steen National Bank to retrieve his escaped Niffler.|
|Lord Voldemort||31 October, 1981||Used this spell to break into the Potters' house and murder James and Lily Potter. He also attempted to murder their son Harry Potter.|
|Albus Potter||After time-travelling to the day his grandparents were killed, Albus Potter unlocked the doors of St Jerome's Church in order to let Harry Potter's friends come and help him to duel Delphini.|
|Hermione Granger||1991||She used it to open a forbidden entrance on the Third-floor corridor of Hogwarts Castle.|
|6 June, 1994||She used it to open the window to Professor Filius Flitwick's office to rescue Sirius Black.|
|2 August, 1997||She also used it to open Regulus Black's bedroom in 12 Grimmauld Place.|
|Death Eaters||18 June, 1996||One of the Death Eaters used this spell to open doors shut by the D.A..|
|St Mungo's staff||Unknown||The Janus Thickey Ward at St Mungo's Hospital for Magical Maladies and Injuries can only be entered by using this spell. Healers and visitors may enter, but patients are unable to get out.|
|Scorpius Malfoy||1 September, 2020||While at the Ministry of Magic under the disguise of the trio, Albus Potter, Scorpius Malfoy, and Delphini need to get into the Minister for Magic's office. Scorpius casts this spell, and it is successful.|
|He eventually found that all wizarding households placed an Anti-Alohomora Charm on their doors and could no longer unlock their doors.|
|Queenie Goldstein||7 December 1926||Tried to unlock Percival Graves' office at the Magical Congress of the United States of America using this spell and Aberto, discovering he had secured it with advanced spells.|
|Hogwarts staff||1991||The door guarding the Philosopher's Stone was protected against the Unlocking Charm; a winged key was necessary to open it. A single door in the Department of Mysteries was impervious to this spell as well; it may be presumed that it opens in the room where the Ministry of Magic studies the power of love.|
|Hermione Granger||1992||Hermione tried to use Alohomora on the locked door in the Flying Key room, but the door could only open with the key.|
|Harry Potter||1 September, 1996||Harry tried to use the spell on the Hogwarts gates with no effect since Albus Dumbledore had bewitched them.|
|Dolores Umbridge||1996||Harry Potter assumed that Umbridge's office door had been bewitched so that this spell wouldn't work.|