Iron Knuckle is an enemy and often mini-boss from the Legend of Zelda series. Even though it's bark is worse than it's bite, it's still a menacing foe.
I remember Iron Knuckle the most in Ocarina of Time near the end of the Spirit Temple. I loved defeating the biggest one who was actually a hypnotised Nabooru.
Remembering this great scene makes me want a 3DS so I can play the Ocarina of Time remake.
I wasn't terribly impressed by their cameos in Majora's Mask though.