Nearly everything we learn about Voldemort in Harry Potter and the Sorcerer’s Stone is secondhand. The book begins with Voldemort’s failed attempt to kill baby Harry and his subsequent disappearance. We know he wants to conquer the wizarding world and that he has evil methods and intentions. He kills anyone who resists him until he is inexplicably stopped by Harry. Most witches and wizards are so afraid of him that they will not say his name out loud. Many characters refer to Voldemort only as You-Know-Who. Even after his disappearance, powerful wizards like Dumbledore are wary that Voldemort will be back to complete his goal eventually.
Throughout the book, Harry learns bits and pieces about Voldemort and why everyone is so afraid of him. Voldemort was once a student at Hogwarts, but he practiced so much dark magic by the time he killed Harry’s parents that he was not considered fully human. The Malfoy family followed Voldemort but claimed he had bewitched them after he disappeared. Harry even suspects Snape of following Voldemort and trying to use the Sorcerer’s Stone to bring him back to life.
At the end of the book, we learn that Voldemort has indeed been seeking the Stone to bring himself completely back to life, but it is Professor Quirrell rather than Snape who has been helping him. Whatever is left of Voldemort after he couldn’t kill Harry attaches itself to Quirrell and uses Quirrell as sustenance. Voldemort does not reward Quirrell’s loyalty but punishes him for failing to succeed. Voldemort makes Quirrell kill unicorns so he can drink their blood. He also leaves Quirrell to die after Harry discovers him and keeps him from attaining the Sorcerer’s Stone. Even in his weak state, Voldemort’s shadow hangs over the story. His brief introduction at the end of the book sets up the tension for the future of Harry’s story because it confirms Voldemort still intends to regain power. Voldemort’s connection to Harry fates the two of them together from Harry’s infancy through the whole book series.