Who is Hal Incandenza from Infinite Jest: A Novel and what is their importance?

Hal Incandenza is the son of James and Avril Incandenza and the brother of Mario and Orin. His is very intelligent but insecure about this fact. Theremore, his mental stability deteriorates as the novel goes on. Eventually, when he tries to talk, no one can understand him, although it is not clear how this happens. Hal is a frequent marijuana user. His withdrawal from the drug may have played a part in his condition. He enjoys keeping his marijuana use from his mother, who is paranoid about her sons keeping things from her.