Helmaroc King

The Helmaroc King, also known as the Helmasaur King is a large creature wearing a strong mask that can be broken with enough hits from a Hammer. It has notably appeared both as a large Helmasaur and a large Kargaroc in different games, hence the varying English names, but even then, they are officially considered different interpretations of the same entity.

The Legend of Zelda: A Link to the Past
The Helmasaur King is the boss of the first Dark World dungeon, the Palace of Darkness. To attack, it swings its spiked tail around the room and can breathe splitting fireballs. Using the Hammer or Bombs on its mask repeatedly will destroy it, revealing its face underneath. Its face has a large green gem on the forehead that can be hit with any attack to hurt it. Once it is defeated, Link acquires the first Maiden-containing crystal.

In the Game Boy Advance enhanced port, an alternate, stronger, green version of the Helmasaur King is in the new Palace of the Four Sword. After the mask is destroyed, instead of fireballs, he will spawn Helmasaurs to attack Link, and once the gem is damaged enough, the mask will repair itself. After it is destroyed again, the gem's place will instead be taken up by a large third eye, resembling that of Vitreous. In this battle, the gem will not be damaged by arrows, but the eye will be immediately destroyed if hit with a Silver Arrow.

The Legend of Zelda: The Wind Waker
Reimagined as a huge bird, the Helmaroc King acts more directly as Ganondorf's minion. He steals maidens from across the Great Sea, with Ganondorf hoping to find the current iteration of Princess Zelda. He manages to pursue the correct one, pirate Captain Tetra to Outset Island, but from there instead grabs Link's sister Aryll, starting his quest. While exploring the Forsaken Fortress where Aryll is imprisoned for the first time, the Helmaroc King can be seen in a giant nest throughout. Once Link climbs to the holding cell, the Helmaroc King grabs him, shows him to Ganondorf, and then tosses him away at his orders.

Later in the game, when Link returns to the Forsaken Fortress and frees the girls with the help of the pirates, the Helmaroc King ambushes him again, and Link mist climb to the top of the tower while water rises. Once at the top, the battle will start. In battle the Helmaroc King can fly about and attempt to scratch, peck, or blow Link into the spikes around the arena. Whenever he pecks, his beak will get stuck in the ground, allowing Link to use the Skull Hammer on his mask, damaging it. Once the mask is destroyed, he is shown having red eyes and a yellow crest. Hitting him enough times further will defeat him, causing him to explode. Unlike other bosses working for Ganondorf, he is not encountered in the boss rush in Ganon's Tower.

The Legend of Zelda: Four Swords Adventures
The Helmaroc King appears as a boss on The Mountain Path. It is capable of swooping around and dropping rocks. Here, bombs must be used to knock it out and destroy its mask, after which the swords can be used to damage it. Unlike most entities in the game, it is modeled, and only appears as an icon of its head on the Game Boy Advance screen.

The Legend of Zelda: A Link to the Past comic
Multiple copies of the unmasked Helmasaur King appear and are called "Gleeocks." An Eyegore sends them after Link after it catches him attempting to blow up the Palace of Darkness by igniting the Firecorn stockpile within using a Hinox bomb.

Hyrule Warriors Legends / Hyrule Warriors: Definitive Edition
The Helmaroc King, now working for Phantom Ganon, appears in the new The Wind Waker-inspired chapter as a boss, and is again weak to the Skull Hammer. It is capable of the same attacks it can do in The Wind Waker, though some have been adjusted to fit the new gameplay style and battlefield size.