Lord Voldemort

"Avada Kedavra!" — Lord Voldemort's signature spell, the Killing Curse.

Lord Voldemort (a.k.a. the Dark Lord, Tom Riddle and He-Who-Must-Not-Be-Named) is an evil Dark wizard who is responsible for the murder of James and Lily Potter, and attempted murder of Harry Potter.

Harry's Destiny
On Halloween, Lord Voldemort and a Death Eater named Loki Kermit appear in London and start causing havoc and destruction, searching for a baby named Harry Potter for some unknown reason. He destroys almost everything, including Muggles. He uses the Killing Curse several times before meeting up with Wormtail, who tells the Dark Lord the whereabouts of Harry, and Voldemort makes Wormtail a Death Eater, before vanishing.

He appears at the Potters' house, where he kills James Potter mercilessly. He then goes upstairs and faces Lily and Harry Potter. Lily defends Harry and prepares to attack, but realises she only has a rubber duck and she is murdered by Voldemort. Lord Voldemort then shoots the Killing Curse at Harry, but it rebounds off his forehead, hits the lamp on the ceiling and hits the Dark Lord in the face, killing him.

Stone
Hagrid reveals that someone, or something, has been sucking the blood of the unicorns. When Harry, Ron, Hermione and Draco Malfoy get detention, they go with Hagrid into the Forbidden Forest and split up to search for any unicorns. However, Harry and Draco find Lord Voldemort about to feed on a unicorn. Draco flees, and Lord Voldemort flies towards Harry, but is scared off by Firenze, who reveals that unicorn blood can keeps someone alive even if they are an inch from death.

In the end, the trio find Professor Quirrell going into the room with the three-headed dog, Fluffy. They follow him, and discover that Quirrell had put a harp there to make Fluffy fall asleep. However, Quirrell sees them and destroys the harp before going down the trapdoor, making Fluffy wake up. The trio escape Fluffy's clutches and go down the trapdoor. They face many challenges down there, each one set up by a teacher. Harry and Hermione go into the last chamber and confront Quirrell who is looking at the Mirror of Erised, then he tells Harry to look into the Mirror. When the Philosopher's Stone appears in Harry's possession, Quirrell gets angry and reveals that he is Lord Voldemort, possessing Quirrell's body. Harry fights off Lord Voldemort's elemental powers, and destroys Quirrell's body by touching him. However, Voldemort's ghost appears and scares Harry, making him faint. He then attempts to collect the Stone, but he can't touch it as he is intangible. Angry, the Dark Lord retreats...

Chamber
When Lucius Malfoy slips a strange black diary with Salazar Slytherin on the back of it, inside the diary is a piece of Voldemort's soul named Tom Riddle, which possesses Ginny, and makes her open the Chamber of Secrets. There, Ginny (possessed by Tom) awakens the Basilisk, and makes it petrify Mudbloods in the school.

The fragment of the Dark Lord's soul convinces Harry that he is the good guy by framing Hagrid and accusing him of opening the Chamber of Secrets.

Later, in the Chamber of Secrets, Harry confronts Tom once more, who is revealed to be draining the life force of Ginny and Harry realises that Tom Riddle is a fragment of Lord Voldemort's soul. Tom summons the Basilisk to kill Harry, but when Harry kills the Basilisk with the Sword of Gryffindor. Ginny discovers that if the diary is hurt, so is Tom, and uses the diary to hurt Tom in various ways before Harry uses a Basilisk fang to destroy the diary, destroying Tom.

Prisoner
When Dobby faces his Boggart, it turns into Lord Voldemort, but Dobby turns the Dark Lord into an infant and sends it to Wormtail in exchange for money to start making a living.

Goblet
Lord Voldemort is revealed to still be in his infant form, being looked after by Wormtail, Barty Crouch Junior and Nagini. He sabotages the Tri-Wizard Tournament and rigs the events so that Harry is teleported to a graveyard. Lord Voldemort's infant form is put into a cauldron, along with the skull of Tom Riddle, the hand of Wormtail and Harry's glasses. Lord Voldemort is resurrected and duels Harry, but is defeated and Harry escapes. Voldemort, however, kills Cedric Diggory just in time.