Severus Snape was a close friend of a person.
 (Towards the end of the book, Harry learns that this was Snape's Patronus, taking the same shape as Harry's mother Lily's Patronus, a visible sign of his lifelong love for Harry's mother, and that Dumbledore had asked Snape to ensure that Harry gained possession of the sword
 James realised the danger and stopped Snape, saving his life; this is the incident Dumbledore referred to at the end of the first book

