Dr. Huntoon was an old associate of John Constantine and oversaw his recovery from the incident at Newcastle. Despite this, Huntoon and Constantine have a disdain for eachother since Constantine ended up with a girl Huntoon whom liked. Huntoon has become a crackpot psychologist/media star who promotes his cynical view of super-heroes in his book "POW Psychology". When he later appeared in the second issue of Neil Gaiman's SANDMAN he had become the director of Arkham Asylum.
Notable appearances in SWAMP THING:
SWAMP THING #66 "One Flew over the Cuckoo's Nest"
To Dr. Huntoon's delight, Batman delivers Killer Croc to Arkham Asylum, but not without sustaining a few injuries. Batman does not meet ST, but Constantine is there.
SWAMP THING #70 "The Secret Life of Plants"
#71 "Fear of Flying"
Constantine coaxes information from Huntoon.
SWAMP THING #79 "Waiting for God-oh!"
Huntoon attends a Superman press conference and argues with Lois Lane.