Dedede has been the only other consistent character that's been a factor in the outcome of Kirby games other than Kirby himself. Aside from the fact that he's not as cool as MetaKnight from a general standpoint, he's every bit more valuable as a Kirby character so far in the series. Toad isn't a big part of Mario. Goroh doesn't really make Falcon a bounty hunter. Slippy doesn't make Fox any better of an Arwing pilot, all while Dedede makes Kirby a hero.
Dedede is as to Kirby as Bowser is to Mario, in this sense. Most of the time, he is the villain. Sometimes, he is an ally, but, except for one or two games, he is always present. The difference is that Dedede usually allies with Kirby because he finds a greater benefit in helping the puff out. As King of Dreamland, if DL blew up, he wouldn't be king anymore, so he often helps Kirby prevent this scenario from playing out. Whenever Kirby isn't saving the entire planet from something outside, he's stopping Dedede from eating everything in sight.