Professor Horace Eugene Slughorn was a masterful Potions master and, for two separate tenures, the Head of Slytherin House at Hogwarts School of Witchcraft and Wizardry. A bon vivant with a love for comfort, luxury, and influence, Slughorn was known for his “Slug Club”, an exclusive group of students he “collected” based on their talent, ambition, or famous connections. Though not malevolent, Slughorn's desire for a quiet life and his deep-seated shame over a past mistake made him a reluctant figure in the Second Wizarding War. He possessed the crucial memory that revealed Lord Voldemort's secret to immortality, the Horcruxes, making him a key target for both Albus Dumbledore and the Death Eaters. His eventual decision to aid the fight against Voldemort demonstrates a complex character who, despite his flaws, ultimately chose to do what was right.
Professor Slughorn's first period as Potions Master and Head of Slytherin House lasted for many decades. During this time, he established the “Slug Club”, a collection of his favourite students invited to lavish dinners where he could build a network of influential future witches and wizards. He taught many notable individuals, including Lucius Malfoy and Harry Potter's mother, Lily Evans, whom he considered one of the most brilliant and charming students he ever had. His most fateful student, however, was Tom Riddle. Flattered by the young Riddle's talent and ambition, Slughorn confided in him the highly dangerous and obscure magic of creating a Horcrux. Overcome with shame and terror at what he had enabled, Slughorn later used a Memory Charm on himself to alter the memory, obfuscating the most incriminating parts of their conversation. He retired from Hogwarts shortly after Lord Voldemort's first fall from power, succeeded by Severus Snape.
Following his retirement, Slughorn went into hiding after the confirmed return of Lord Voldemort, correctly fearing that his former student would seek to recruit him or silence him permanently. He lived a nomadic life, moving between Muggle houses and employing elaborate charms to remain hidden. In the summer of 1996, Albus Dumbledore and Harry Potter tracked him down to the village of Budleigh Babberton. To persuade the comfort-loving Slughorn to return to Hogwarts, Dumbledore used Harry as “bait,” knowing Slughorn could not resist the chance to “collect” the Chosen One. Slughorn agreed to resume his old post as Potions Master, partly for the perceived safety of Hogwarts and the allure of having Harry in his class.
Throughout the school year, Harry Potter was tasked by Dumbledore with retrieving the true, unaltered memory of Slughorn's conversation with Tom Riddle. Slughorn repeatedly evaded Harry's attempts, crippled by his shame. Harry finally succeeded after taking a dose of Felix Felicis, which led him to Aragog's funeral. During the event, a tipsy and emotional Slughorn, moved by Harry's words about his mother Lily Evans, finally relented and gave Harry the true memory. This memory was the final piece of the puzzle Dumbledore needed to confirm the number of Horcruxes Voldemort had created. During the Battle of Hogwarts, Slughorn initially evacuated the younger students and appeared to leave with the Slytherins who chose not to fight. However, he later returned with reinforcements from Hogsmeade. He demonstrated immense bravery and powerful magic by dueling Lord Voldemort directly, alongside Minerva McGonagall and Kingsley Shacklebolt.
Slughorn is described as an enormously fat, short man with a shiny, bald head and a prominent, walrus-like moustache. He has a penchant for luxurious clothing, such as a green velvet smoking jacket and an embroidered nightcap. His personality is dominated by his love for comfort, influence, and the finer things in life. He is a classic networker, using his charm to cultivate relationships with those he deems important. While this makes him appear opportunistic and self-serving, he is not a cruel person and shows genuine fondness for his favourite students, especially Lily Evans. He is prone to cowardice and fear, as shown by his years in hiding and his modification of the Horcrux memory. However, his actions at the Battle of Hogwarts prove that, when truly tested, he possesses considerable courage and loyalty.