The character Harry Potter apparently appeared in the 1986 film Troll starring Noah Hathaway and June Lockhart and directed by John Carl Buechler. Not the same Harry Potter, although both films do share a commonality in their use of magic.
Harry Potter (Noah Hathaway) and his family move into a new neighborhood, and Harry meets an old woman Eunice St. Clair (June Lockhart), who turns out to be a witch, and she and Harry enter the Troll’s fairy world to try and stop it from turning other people into plant pods. Compelling.
I’ve never actually seen the film, but I was reading about it on wikipedia and IMDb, and the entry on wikipedia says the Harry Potter in Troll is also a dark haired young boy about the same age as the Potter from J.K. Rowling’s novels, and he enters a world of magic and meets wizards and fights a troll.
Supposedly, John Buechler is doing a remake of Troll, with the name Harry Potter still used for the main character.