Rebonack

Rebonack, also known as simply Ironknuckle or Guardian Ironknuckle, is a blue Ironknuckle (or perhaps multiple identical ones) who rides a floating representation of a horse. He is fought in Zelda II: The Adventure of Link.

Zelda II: The Adventure of Link
In Zelda II: The Adventure of Link, Rebonack is fought in the Island Palace as the boss, and later twice in the Three-Eye Rock Palace as a miniboss. When the battle starts, the boss music plays, but he is not present. After a short amount of time, he charges in from offscreen on his horse. Throughout the battle, he keeps charging on, off, and across the screen. To damage him, Link must perform a Down Thrust onto him. After his health meter is mostly depleted, he dismounts, which resets his health meter. From here, he acts like a normal blue Ironknuckle. Depleting his health bar all the way from this point causes him to explode.

The Legend of Zelda: Breath of the Wild
Rebonack does not appear directly in The Legend of Zelda: Breath of the Wild, though the Rebonae Bridge is named for him. Other nearby bridges are named for other bosses in Zelda II: The Adventure of Link.

Captain N: The Game Master
In Captain N: The Game Master, Ironknuckle appears in the episode Quest for the Potion of Power, where he is the guardian of the eponymous potion. Link, Zelda, and Kevin find him at the Island Palace, but while he is distracted with them, Eggplant Wizard and King Hippo steal the potion. Ironknuckle grabs Zelda, and Link and Kevin use their respective weapons to fire upon him, causing him to drop Zelda, who joins in on the attack, defeating him for good.