It is known from early on in the story who the shadow is in the story. He who should not be named, Lord Voldemort is the villain. He is the most powerful dark wizard. Throughout the magical world, he has caused many deaths, including Harry's parents' death. He is all definitions of an evil person person. He wanted to create a pureblood race of wizards and witches, therefore, eliminating muggles(two ordinary parents) and halfbloods(pureblood parent and ordinary parent).  In the movie, his goal was trying to go after the Sorcerer's Stone to turn into human form again and try to kill Harry Potter.