Galacta Knight did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Galacta Knight, also known as the Aeon Hero, is a reoccurring boss from the Kirby series, acting as a rival to Meta Knight. He is often referred to as the Greatest Warrior in the Galaxy, most notably in his theme, and was sealed away by the ancients because of his great power. Galacta Knight first debuted in the Nintendo DS remake of the popular Super Nintendo Entertainment System title Kirby Super Star Ultra, where he served as the final boss of the Meta Knightmare Ultra sub-game after Meta Knight summoned him. He also appears as a boss in The True Arena.
From then on, he's made appearances in other games such as Kirby's Return to Dream Land as a boss in the True Arena, Kirby: Planet Robobot as the final boss of Meta Knightmare Returns and a boss in the True Arena, and finally Kirby Star Allies where he is briefly seen before transforming into Morpho Knight. He also appears as the final opponent of Super Kirby Clash under the name of Aeon Hero, and assumes two powered up forms: light and dark.
Galacta Knight has a similar fighting style to Meta Knight, although he has a few energy moves to his arsenal such as Crescent Shots, Flame Spine and Revolution Sword. Galacta Knight can even rip open a hole in the fabric of space and time to fire a large laser.