He is a Healslime who seeks to become a human. Whether this is the same character in each appearance or just a homage is unknown, and left open to player interpretation.
Ragnar McRyan first encounters him in his chapter within the Auld Well, at which point he joins the party. Healie uses his knowledge of local geography to help Ragnar in his quest to locate the missing children of Burland. He proves to be an extremely useful ally in battle, as Ragnar is incapable of using any spells, so the only way he can heal himself without Healie's help is with items such as Medicinal herbs. Healie can also contribute to combat, though the damage he is capable of dealing is fairly unimpressive. As an AI-controlled character, his behavior is also somewhat random and unreliable.
Towards the end of Chapter 1, he states that he has resolved to become a human. He apparently continues to travel with Ragnar because they can be found together in Chapter 5, shortly before the fight with Balzack. Healie has succeeded in becoming a human through unknown means and has taken on the sprite of a bard. This, however, is the last he is seen in the game; after Ragnar joins the Hero's party, it seems Healie continues his travels alone.
In this game, when interacting with certain elements in Burland during the night with Healie in the party and then using Party Chat, he reveals that he, Guru Curu the Cureslime, and Mary Curey the Medislime are his friends and he has not visited them in quite awhile. Guru Curu can be found at Canalot at night inside a church while Mary Curey can be found in the later stages of Pioneer Town.
"I met another human. He was wearing armour like you. I wanted to goo with him, but he refoozed. Maybe he didn't think a slime was goo enough for him? I was very hurt... (slurp)"
"That's him! That's the human who refoozed to take me with him! What a horrible man! (slurp) But I suppooze he did me a favour. If I had gone with him, I'd never have met you!"
In the SNES version of VI, Healie can be randomly recruited when a Healslime is defeated in battle and one of the party members is a rank 2 Monster Master.
In the Nintendo DS remake of VI, Healie can be recruited in Clearvale after obtaining the Flying Bed. In the ending credits, if Healie is interacted with in Somnia, he mentions his desire of becoming a human, foreshadowing his role in Dragon Quest IV.
Aside from class abilities, Healie learns several spells on his own. Along with Curie, Healie is one of the only two party members that can cast Omniheal.
Healie appears as a A-rank member of the Slime family as part of the limited True Dragon Quest IV event, where he can be recruited during the event's story. He joins the player in Chapter 2, Episode 1: A Cry from a Well of the event quests and he can be fully awakened by collecting Healie Crystals from clearing the stage on any difficulty. Healie also stars in his own Battle Road.
Helpful Healie: When an ally is attacked by enemy: Heals with Wartime Midheal if ally is within 1 to 2-space range, 3 times per battle / Healie Multiheal Recovery +5% / Stats Up
Leader Perks
First
Raises healing ability recovery of all allies, including himself, by 5% in a 5x5 square around him.