Sidney "Sid" Phillips is the main antagonist of Toy Story. He is mentioned by Buzz in Toy Story 2. He also makes a cameo in Toy Story 3. He is the only person who knows toys are alive.

Sid was introduced in the beginning of the film as a toy terrorizer when he exploded aCombat Carl with an M-80, with his toy-chewing dog Scud by his side. Andy's toys were surprised to see him back at his old habits so soon, assuming he got kicked out of summer camp early this year. Later that day, when Andy and his family went to Pizza Planet, Sid was also there. After playing Whack-an-Alien, the Crane Game caught his attention. After grabbing a Alien, Buzz Lightyear was put in view. He then went after him, getting not only Buzz, but Woody hooked onto his foot as well (Woody tried to save Buzz, but the Aliens wouldn't let him).

After skating back home with his new toys in his backpack, he was immediately greeted by Scud, whom he gave the alien to viciously chew. Then, seeing his sister Hannah with her Janie doll, he snatched the toy and ran up to his room, slamming the door in Hannah's face. He then pulled out his Pterodactyl toy as he played doctor for his "double-bypass brain transplant." With Sid gone, Woody explored his room to search for a way out, but found the door locked and unable to escape. Trying to find another way out, he then discovered that Sid had taken toys apart and assembled them back together in weird combinations, much to Woody's horror.

More Info: pixar.wikia.com