All the Kirby characters clearly have this role no doubt.
However, the ones with the most impact other than them are Wario, Ness and Ike, and ill explain why.
Ness is clearly important because he was the one who saved Lucas and got turned into a trophy, and ended up waking up and waking Dedede, who showed them how to save the others.
Wario got trophies, which meant Dedede could take them.
Many people will argue with me on Ike, but IMO Ike saved Marth and Metaknight, and Metaknight is a main character. Without Metaknight they wouldn't have halberd, and that would be bad.
Edit: yay someone thought of Ike already!