Knuckles the Echidna is a few of Sonic the Hedgehog's original rivals, other then Shadow and Silver. He first appeared in Sonic the Hedgehog 3, stealing Sonic's Chaos Emeralds. He's also an echidna. He's also incredibly strong, and 16 years old. He also has both Super and Hyper transformations, unlike Tails.
Knuckles has starred in many Sonic games, since the first game he came out. However, he couldn't be played, until Sonic and Knuckles, which also had him playable in Sonic 3. Knuckles is noted for his strength, which showed in the first game he was in, and Sonic Heroes. He can break through walls, without spindashing into them, he just has to punch them.Knuckles has gotten mixed reviews, sometimes bad, but mainly good. His popularity has grown since then, and has really grown since Sonic the Hedgehog 3 (and Knuckles).