Voldemort
Background
Tom Marvolo "Lord Voldemort" Riddle is a deceased evil wizard. He died after killing Lily Potter and James Potter and then attempting Harry Potter. Voldemort is also known as "He Who Must Not Be Named".
During the events of Harry Potter and the Sorcerer's Stone (2001) played by Richard Bremmer and the Ian Hart
In the Forbidden Forest, Harry Potter, Draco Malfoy and Fang come across a robed figure hunched over the wounded unicorn and Fang and Draco run away, leaving Harry. As the robed figure glides towards Harry, Harry is saved by Firenze who warns Harry the forest isn't safe. Harry enters the last room in the area guarded by Fluffy and finds Professor Quirrell staring at the Mirror of Erised. Professor Quirrell tells Harry, Professor Snape was actually trying to save him during the Quidditch match and Snape knew he was up to something. Professor Quirrell wonders how to get the Sorcerer's Stone and a voice suggests he use Harry. Harry looks into the mirror and the mirror shows him the Sorcerer's Stone is in his pocket. Harry lies to Professor Quirrell about what he sees in the mirror and Professor Quirrell removes his headdress, revealing Voldemort's head living on the back of his skull. Professor Quirrell attacks Harry, but Harry manages to kill him when he notices that his touch wounds him and Harry causes Professor Quirrell to dissolve by touching him in the face. As Harry is holding the Sorcerer's Stone, Voldemort's spirit comes at him and Harry goes unconscious.
During the events of Harry Potter and the Chamber of Secrets (2002) played by Christian Coulson
Harry goes into the main chamber of the Chamber of Secrets and finds Ginny Weasley lying on the ground unconscious. Tom Riddle walks up to Harry and tells him as Ginny grows weaker, he grows stronger and it was Ginny that opened the Chamber of Secrets and sent the Basilisk after the Muggle Borns. Tom Riddle then reveals himself to be the younger version of Voldemort. Fawkes flies into the Chamber and drops The Sorting Hat onto the ground. Tom Riddle calls the Basilisk to him and it starts to chase Harry. Fawkes flies and helps Harry by clawing out the Basilisk's eyes. Harry escapes from the Basilisk and the Sword of Gryffindor materializes inside The Sorting Hat. Harry grabs it and uses it to kill the Basilisk, but is wounded in the process. As he is dying from the venom of the Basilisk, he takes the tooth that was impaled into his arm and stabs Tom Riddle's journal with it, destroying the manifestation of Tom Riddle and the journal.