Draco Malfoy is Harry's arch enemy. They despise each other. Draco is uppity and snotty and resents Harry's popularity. He is rich and got on the Quidditch Slytherin team just because his Dad bought them all expensive broomsticks. Harry has gotten into trouble more than once with Draco-related incidents.
Harry, Ron, and Hermione thought he was the Heir of Slytherin that was commanding the Chamber monster to kill. They took a Polyjuice potion and it transformed themselves into Crabbe and Goyle, Draco's thugs who follow him around simply as a threat to anyone who contests Draco.They are not too bright.
As it turned out, Draco had nothing to do with the whole mess. They find this out by talking to Draco as Crabbe and Goyle (they turned into them with the potion), knowing that he would tell them the truth. His Dad had MUCH to do with it, but Draco knew nothing of it, and neither did Crabbe or Goyle.