From WiKirby
Ax Knight is a recurring enemy throughout the Kirby series, debuting in Kirby's Adventure and making its most recent appearance in Kirby Super Star Ultra. It is, relatively, a Kirby-sized creature, sporting a large, purple & gold, spike-ridden helmet with curved horns, and a small, skull-like body. It has unusually hollowed eyes, with red pupils, and wears small, oval, blue-hued slippers and round, white gloves. As its name indicates, Ax Knight is armed with a battle axe.
Along with Javelin Knight, Mace Knight and Trident Knight, Ax Knight is part of a small group of combatants, led by Meta Knight, appropriately named Meta-Knights. As such, it is one of the enemy types encountered during a Meta-Knights Mid-Boss fight, and normally must be destroyed at least once, in order to win the battle. On very rare occasions, it can also be found outside of a Mid-Boss encounter, portrayed as a regular enemy.
Aside from battling Kirby, one particular Ax Knight assists Meta Knight inside the main cabin of the Halberd in Revenge of Meta Knight.