Walter Huff is a mysterious figure who is the primary antagonist in the book. He is a serial killer who sends postcards to his victims before killing them.
Jason's father is a former FBI agent who is investigating Huff's crimes. He doesn't share any specific information about Huff with Jason, likely for safety reasons and to avoid influencing Jason's investigation.
The only information that Jason receives about Huff is from the postcards he sends and the news reports about his crimes. This is part of what makes the book so suspenseful, as Jason is constantly trying to piece together information about Huff and his motives.