Marx, or マルク(Maruku) is a character from the Kirby franchise!
He first appeared in 1996's Kirby Super Star. He is best known for tricking Kirby into making a wish on the Comet Nova, only to steal the wish and try to take over Kirby's home planet. Upon making this wish, he grows a pair of skeletal wings, becoming the final boss of the game. In the 2008 re-make Kirby Super Star Ultra, he re-appears as the final boss of the True Arena in the form of Marx Soul.
Ten years later, he appeared in 2018's Kirby Star Allies as a playable Dream Friend. The same year, he reprised his role as a final boss in Super Smash Bros. Ultimate.
Despite first appearing in 1996, the first major Marx merchandise was the plush produced in 2017, probably to boost his relevancy before his appearance in Kirby Star Allies. The vast majority of Kirby merchandise is only released in japan, and that holds true for the merchandise on this site.
For more information: Kirby Fandom wiki page | WiKirby Page | Wikipedia Blurb