Why Did Voldemort Kill Harry Potter's Parents?

In the "Harry Potter" books — and the film franchise they spawned — Harry, played on-screen by Daniel Radcliffe, faces off against a number of different villains and antagonists (too many, one could argue, for a kid who's not even 18 by the time the story ends). None of them loom quite as large as Voldemort, though. Originally named Tom Marvolo Riddle and played, after he regains corporeal form in "Harry Potter and the Goblet of Fire," by Ralph Fiennes, the Dark Lord was one of the most feared and evil wizards in the entire wizarding world ... Until he got his butt kicked by a baby. Let me explain.

Before the proper narrative of "Harry Potter" even gets going, Voldemort takes it upon himself to "visit" the Potter family home in the sleepy wizarding hamlet of Godric's Hollow so that he can murder the trio, including baby Harry and his parents James (Adrian Rawlins) and Lily (Geraldine Somerville). So, why does Voldemort attempt infanticide and murder two people in the process? Why doesn't it work — or more specifically, why is one of the most powerful wizards around unable to take out a little baby? How does this affect Harry's life, and how does he eventually bring Voldemort down for good? Here's the full breakdown.

By the time Lily and James Potter know they're in Voldemort's crosshairs — thanks to their work with the Order of the Phoenix, a resistance group fighting against the Dark Lord's regime — they realize they need to hide their home using enchantments and protections in Godric's Hollow. Seeking help, they turn to Albus Dumbledore (played by Richard Harris and then by Michael Gambon after Harris passed away in 2002). Dumbledore offers to serve as the Potter family's "Secret-Keeper": if they cast the Fidelius Charm over their home and stay inside, only one person will know where they're hidden, and only their Secret-Keeper can pass the secret to others. But instead of Dumbledore, James and Lily elect to go with Sirius Black (Gary Oldman), James' longtime best friend. 

Sirius then makes a grave error in judgment. Thinking that Voldemort will surely target him because he's a formidable fighter, Sirius convinces the Potters to make their weaker friend Peter Pettigrew (played on-screen by Timothy Spall) the Secret-Keeper instead, thinking that nobody, especially Voldemort, will ever suspect that Peter holds this secret. Unfortunately for Sirius and literally everybody involved, Peter (more commonly known as "Wormtail," because he's an Animagus who can transform into a rat) is in cahoots with Voldemort and gives up James and Lily's location more or less immediately. 

The reason Voldemort targets a young couple and their one-year-old baby comes back to one specific moment: a prophecy delivered by Sybill Trelawney (Emma Thompson), the future Divination professor at Hogwarts School of Witchcraft and Wizardry. Trelawney's predictions are typically pretty dubious, but when she goes into a sort of trance, you know it's the real deal. This is what happens when she meets Dumbledore in a private room at the Three Broomsticks in Hogsmeade, at which point she drops this absolute banger of a prophecy: 

"The one with the power to vanquish the Dark Lord approaches... born to those who have thrice defied him, born as the seventh month dies... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives... the one with the power to vanquish the Dark Lord will be born as the seventh month dies...."

Here's the problem. A young Severus Snape — the eventual Potions master at Hogwarts played by the late, great Alan Rickman — is listening at the door on Voldemort's behalf and reports just the first part of the prophecy to his master (meaning the part about being born to "those who have thrice defied him" and "as the seventh month dies"). When Voldemort kills Lily and James, only to end up felled by a literal toddler, Snape, who loved Lily since childhood, is bereft. Under significant duress, he agrees to be a double agent against Voldemort and for Dumbledore for the remainder of his life, protecting Harry in the process.

Aside from only hearing half of a prophecy and rushing to act on it, Voldemort made a second mistake in attacking the Potters — although you could very easily read it less as a "mistake" and more as a "decision." As it happens, there was a second infant hanging around who was born in July whose parents "defied" Voldemort three times: Neville Longbottom (Matthew Lewis), Harry's Gryffindor classmate.

Had Voldemort simply sauntered over to the Longbottom residence on Halloween in 1981 (the date he attacked the Potters) and picked on Neville instead, the books and movies would, I guess, be named after him instead. As Dumbledore tells Harry, though, the reason why Voldemort "picks" Harry is actually quite important. Neville comes from a pureblood family, whereas Harry's mother Lily is Muggleborn — meaning that she apparently had no magical ability until it presented early in her childhood, surprising her non-magical family. Voldemort's parents, a wealthy Muggle named Tom Riddle Jr. and a witch named Merope Gaunt, bore a stronger similarity to Harry's than Neville's, so Dumbledore surmises that Voldemort "marked" the child most similar to him.

In any case, Voldemort ensures that the prophecy refers to Harry, and not Neville, when he attacks the Potters. So, how and why does Harry survive the night even though his parents perish?

After Voldemort enters the Potter home and kills James, Lily barricades herself in Harry's room, putting her body between herself and her son. Voldemort easily breaks down the door and tells Lily to "stand aside," because he's really just there to kill a tiny human being who is (probably?) still wearing diapers, but Lily won't budge. Despite the fact that he repeatedly tells Lily she doesn't have to die, Voldemort kills Lily to get to Harry and then casts the Killing Curse, "Avada Kedavra," on the baby. The curse rebounds, giving Harry his signature lightning bolt scar and "killing" Voldemort. (He doesn't actually die thanks to his Horcruxes but does lose his human form; I'll circle back to that momentarily.)

So why does this happen? As Dumbledore explains to Harry after his first year at Hogwarts — and Voldemort's next attempt on Harry's life, which involves possessing the body and head of a Hogwarts professor — Lily's sacrifice created a rare and strong magical protection surrounding Harry that basically placed an impenetrable shield between adult Voldemort and baby Harry. Until Harry comes of wizarding age at 17, he has to spend each summer with his mother's sister, his awful Aunt Petunia (Fiona Shaw in the movies) and her odious husband and son. But as Dumbledore explains to both Petunia and Harry, Lily's blood runs in both of their veins ... and he must call the house home at least sometimes in order to keep the protection alive. In "Harry Potter," love is the strongest magic there is, which explains how and why Lily's sacrifice carries such weight.

Here's where things get a little weird. In the fourth book and film, "Harry Potter and the Goblet of Fire," Voldemort sets a wildly elaborate trap for Harry, ensuring that he wins the Triwizard Tournament by placing his name in the titular Goblet of Fire and sending a Death Eater disguised as a Hogwarts professor to basically help him cheat his way through the game. At the end of the third task — a massive maze on the grounds of Hogwarts — Harry and his fellow Hogwarts champion, Hufflepuff student Cedric Diggory (Robert Pattinson), decide to take the Triwizard Cup together and share the glory, at which point they're unexpectedly transported to a second location.

What Harry and Cedric had no way of knowing was that the Triwizard Cup was actually enchanted to be a Portkey (a magical form of transportation). When they land in a mysterious graveyard, they're understandably confused and wary. Tragedy strikes immediately when Wormtail, who revealed himself to Harry in the previous installment ("The Prisoner of Azkaban") as Voldemort's loyal foot soldier, shows up. On Voldemort's orders, Wormtail kills "the spare," meaning Cedric. Harry barely has any time to react before he's tortured repeatedly by Voldemort using two of the three Unforgivable Curses — "Cruciatus," which causes horrible pain, and "Imperius," which offers the spellcaster complete control, are banned in the wizarding world alongside "Avada Kedavra." When Voldemort invites him to fight before his death, Harry decides to die standing like his father before him.

When the two start to duel — Voldemort with "Avada Kedavra" and Harry with the Disarming Charm "Expelliarmus" — something really strange happens. The wands, thanks to their twin phoenix feather cores, connect, and specters of Voldemort's victims — including Cedric and Harry's parents — emerge from the Dark Lord's wand, swarming him as Harry grabs Cedric's body and the Triwizard Cup and escapes. 

After dueling Voldemort in "The Goblet of Fire," Harry encounters Voldemort directly once again in the fifth book and film, "The Order of the Phoenix," but has to basically do a whole host of side quests before facing off against the Dark Lord for real in "Harry Potter and the Deathly Hallows." (The film franchise splits "Deathly Hallows" in half, so the showdown happens in "Part 2.") Before Harry can truly defeat Voldemort, he has to hunt the Dark Lord's Horcruxes — magical items that contain pieces of Voldemort's soul — and destroy them; unfortunately for Harry, one of those Horcruxes resides within him after Voldemort's attack when he was a baby. 

Harry picks up one of the three Deathly Hallows — specifically, the Resurrection Stone — and heads towards Voldemort's position in Hogwarts' Forbidden Forest, preparing for his death (based on the prophecy, "neither can live while the other survives"). Using the Stone, he summons the ghosts of his lost loved ones, including James and Lily, who, even in spectral form, encourage him and lend emotional support. Harry allows Voldemort to cast the Killing Curse, and after a brief stay in a sort of limbo — with Dumbledore's ghost, no less — Harry returns to the world of the living and duels Voldemort for the final time.

Moreso in the book than in the film, Harry delivers a rousing monologue to Voldemort about how love is the only magic the Dark Lord can't possibly understand and casts Expelliarmus for the final time against his nemesis, rebounding Voldemort's Killing Curse once again. Voldemort's defeat is at Harry's hands, yes, but it traces back to Lily Potter's sacrifice ... and explains how, when Voldemort chose to attack the Potters, he signed his own death certificate.