Rick Veitch created Dr. Huntoon in Swamp Thing #66 dated November 1987.
Major Story Arcs
Dr. Huntoon is seen during Swamp Thing at Arkham Asylum and delighted when Batman brings in Killer Croc for him. We later learn he is an old school associate of John Constantine's with whom he is on bad terms due to John getting with a girl he liked named Diane. John refers to him as "Piggy". He can be seen later at a Superman convention.
After the Newcastle incident, Huntoon was John's main caretaker during his stay in Ravenscar mental hospital. He appears the Hellblazer issue #8 where we see a flashback of him giving John electroshock therapy.
He later appears in The Sandman at Arkham Asylum with John Dee and in Animal Man with the Psycho Pirate.
He famously wrote the book "Pow! Psychology: Understanding the Super-Men (and Women)" which featured alleged nude photos of the Teen Titans, though John Constantine claims they were faked.
Dr. Huntoon appears briefly in the pilot episode of NBC's Constantine "Non Est Asylum" as a psychiatrist at Ravenscar. He interviews John about the Newcastle incident, though this version doesn't appear to have known John before hand.
He later appeared in a promotional video for the series which featured recorded personal log footage from Huntoon's interviews with John at Ravnescar. He appears to be attacked by something at the end of the video.