Galacta Knight is a powerful warrior who was sealed away due to his power that is summoned by Meta Knight, and is the final boss of the "Meta Knightmare" mode in the video game Kirby Super Star Ultra. Galacta Knight is also the penultimate boss of the "True Arena" mode, where he fights Kirby as well.
Galacta Knight reappears in Kirby's Return to Dreamland in the "True Arena", fought shortly before Magolor. Other than that, Galacta Knight has no impact on the story, but is speculated to be the one who told Magolor of Kirby's exploits, which would make him the Bigger Bad of the story.
Galacta Knight appears once more as the hidden final boss and Bigger Bad in Kirby: Planet Robobot in Meta Knight's story mode, Meta Knightmare Returns. He is summoned from his dimension from the incredibly powerful supercomputer, Star Dream, to challenge Meta Knight in one final battle to see if Meta Knight can become the new admin of Haltmann Works Company. Star Dream notes that Galacta Knight may end up destroying a planet or two, but the results of the battle matter more. Upon being summoned, he turns around and demolishes Star Dream in a single swipe, before unleashing a barrage of all-new attacks on his old nemesis. Upon his third defeat, Galacta Knight is placed into a crystal prison and sent back to his dimension.
He returns as the penultimate opponent to Kirby in the "True Arena", and returns from his prison. Upon his final defeat, he appears to flash around the screen and explode, but reveals that he is not dying and rockets off, escaping once again. His incredible damage done to Star Dream, however, forces it to turn into Star Dream Soul OS, making it Kirby's final opponent in the "True Arena".