Tom Riddle's Diary

• Type: Horcrux, Magical Diary
• Owners: Tom Marvolo Riddle, Lucius Malfoy, Ginny Weasley, Harry Potter, Albus Dumbledore
• Maker: Tom Marvolo Riddle

Tom Riddle's Diary was a small, thin book with a plain black leather cover. It was purchased by a young Tom Riddle from a Muggle newsagent's shop on Vauxhall Road in London. On the inside front cover, the name “T. M. Riddle” was printed. The pages of the diary were seemingly blank and showed no trace of writing, regardless of what had been inscribed within it previously. The diary was enchanted to appear brand new, showing no wear and tear from use. When it was destroyed, a hole was burned clean through its center, and a great deal of a red, ink-like substance, described as being like blood, gushed from its pages, followed by the screams of the Horcrux within.

As Lord Voldemort's first Horcrux, the diary contained a significant and powerful fragment of his soul. Its primary magical properties were geared toward manipulation, possession, and the eventual restoration of its master.

• Two-Way Communication: The diary functioned as a communication device. When a person wrote on its pages, the ink would vanish, and the memory of the sixteen-year-old Tom Riddle preserved within would write back, engaging the user in a persuasive and manipulative conversation.
• Possession: The diary was capable of possessing the individual who confided in it. By feeding on the user's deepest fears and secrets, the soul fragment within the diary could drain their life force and bend them to its will. Through this method, it forced Ginny Weasley to open the Chamber of Secrets.
• Memory Viewing: The diary could show its user specific, curated memories from Tom Riddle's past. Harry Potter was shown a memory in which Riddle framed Rubeus Hagrid for opening the Chamber of Secrets fifty years prior.
• Life-Force Absorption: The ultimate goal of the diary's soul fragment was to siphon enough life from its victim to create a new physical body for itself. It nearly succeeded in doing this with Ginny Weasley before Harry Potter intervened.
• Horcrux Nature: As a Horcrux, the diary tethered Lord Voldemort to life. Its destruction required exceptionally powerful means, far beyond conventional magic. It was ultimately destroyed by the venom from a Basilisk fang, one of the few known substances capable of annihilating a Horcrux.

In 1943, during his sixth year at Hogwarts School of Witchcraft and Wizardry, Tom Riddle created his first Horcrux. After opening the Chamber of Secrets and using the Basilisk to murder a fellow student, Myrtle Warren (later Moaning Myrtle), he performed the dark magic necessary to split his soul and embedded a fragment within the diary. Before his first fall from power, Riddle entrusted the diary to his loyal Death Eater, Lucius Malfoy. He instructed Malfoy that it was a key to reopening the Chamber of Secrets, but did not reveal its true nature as a Horcrux. For years, Malfoy kept the diary, awaiting an opportunity to use it to purge Hogwarts of Muggle-born students. In August 1992, Lucius Malfoy saw an opportunity to both discredit Arthur Weasley and get rid of the dangerous dark object. In Flourish and Blotts, he surreptitiously slipped the diary into Ginny Weasley's cauldron among her secondhand schoolbooks. Ginny began writing in the diary, and the memory of Tom Riddle slowly possessed her. Under its influence, she opened the Chamber of Secrets, unleashing the Basilisk and leaving threatening messages on the castle walls. Terrified, Ginny attempted to dispose of the diary by flushing it down a toilet in Moaning Myrtle's Bathroom. The diary was then found by Harry Potter. He communicated with Riddle's memory and was manipulated into believing Hagrid was responsible for the attacks. Later, a possessed Ginny stole the diary back from Harry's dormitory in the Gryffindor Tower. The soul fragment then lured Ginny into the Chamber, where it began to drain her life to restore its own body. Harry discovered the truth, entered the Chamber, and after a battle with the Basilisk, he stabbed the diary with one of the creature's fangs. The Basilisk venom destroyed the Horcrux, saving Ginny and vanquishing the memory of the young Lord Voldemort. The destroyed diary was shown to Albus Dumbledore, who immediately recognized its profound dark magic and understood it was proof that Voldemort had created more than one Horcrux to achieve immortality.

The diary is the central magical object and antagonist in Harry Potter and the Chamber of Secrets. Its discovery and destruction are pivotal to the plot of the second book. It serves as the first Horcrux that Harry Potter encounters and destroys, establishing the method for how other Horcruxes can be defeated. The diary also provides crucial insight into Lord Voldemort's history, his true name (Tom Marvolo Riddle), his Slytherin heritage, and his malevolent activities as a student at Hogwarts. This encounter marks a significant step in Harry's understanding of his enemy.

• In the film adaptation of Harry Potter and the Chamber of Secrets, the destruction of the diary is more visually explosive. When stabbed, the ghostly image of Tom Riddle is shown screaming and shattering into light, in addition to the inky blood pouring from the book (film).
• A deleted scene from the film shows Lucius Malfoy attempting to plant the diary not in Ginny's cauldron, but inside one of her books in Flourish and Blotts, before being confronted by Arthur Weasley (film).