— Knuckles the Echidna, "Missile Wrist Rampage"
Knuckles is a wild and tough echidna. He is grumpy and doesn't adapt easily. Once he and Sonic were rivals, but their differences have been resolved. He is often jealous of Sonic's free spirit (Rouge once stated that Knuckles had an "inferiority complex") He is famous as a treasure hunter and a master of martial arts. His arms are so powerful that he can shatter rocks. Ever since the big Chaos Control, Knuckles has become dedicated to finding the Chaos Emeralds so he can go back to his job of guarding the Master Emerald.
Knuckles hails from an unnamed world in a parallel dimension to Earth. This is the planet that all of the games other than Sonic Adventure and Sonic Adventure 2 have been stated to take place in. His role is minor until the video game adaptions and then minor again.
In Season 3 after returning home, he joins the heroes gathering the Chaos Emeralds in space. He grows closer to Rouge after this adventure, but back on Sonic's world, he fails to see Chris leaving and declares war on Eggman with the others.
Knuckles bruised by Rouge in Episode 52Knuckles has one weakness; he is quite gullible. The "unseen love" between Knuckles and Rouge grows in Season 3. This includes more yelling, more tricks, and working together to defeat the Metarex.
Knuckles once had to use the Master Emerald to power up the Space Ship Typhoon. At first he was too stubborn to use it, but after a serious beat-down by Amy, Cream, and Cosmo and no help from Sonic, the Master Emerald had to be used. The Emerald dies when powering up the Sonic Overdrive cannon to defeat the Metarex and save Sonic from them in Episode #76. Rouge the Bat has a crush on Knuckles, and he blushes when she flirts with him.
Rouge is Knuckles' rival, especially in treasure hunting. The way Knuckles can punch is just like the way Rouge can kick. The two can get into heated or playful arguments. Rouge constantly teases Knuckles because of his grumpy attitude. In the Sonic X bio, it is revealed that she has a crush on Knuckles, however it is unknown whether Knuckles returns the same feeling for her, but in a few episodes it is hinted that he may like her.
In the episode Volcanic Venture, Knuckles and Rouge had to team up with Sonic to go into a volcano; however the two couldn't get along and were constantly arguing, but Sonic didn't mind it. But somewhere in the end of the episode Rouge flies off, Knuckles asks her where is she going; she said that she'll find Chris, Knuckles tells her to stop, he shyly smiles and says, "Hehe! Good Luck!", Rouge replies that she'll be back and comments that he is "handsome".
In episode 52, Knuckles and Rouge were simply talking to each other, until they came to a heated fight, because Knuckles was making fun of Sonic and Rouge didn't like that and said that she knows that Knuckles actually misses Sonic and he should be lucky that she came and gave him company, Knuckles couldn't admit that fact and said that she is actually the one who is missing Sonic. After brutally hitting each other, they see Super Sonic flying in the sky, they stopped fighting and Rouge asked that it is useless to fight like this, Knuckles comments that Rouge looks "awful" with dirt covered on her face, Rouge then jumps on Knuckles with the camera facing the moon, and it is believed that she's tickling him (kissing him in the Japanese version), since Knuckles was heard laughing hysterically and shouting. "Rouge, stop!! That tickles!" Even if they really are fighting, it's in a playful manner.
- Sonic the Hedgehog (Friendly Rival and good friend)
- Miles "Tails" Prower (Best Friend)
- Amy Rose
- Cream the Rabbit
- Christopher Thorndyke
- Shadow the Hedgehog
- Vector the Crocodile
- Espio the Chameleon
- Charmy Bee
- Vanilla the Rabbit
- Big the Cat
- Tikal the Echidna
- Rouge the Bat
- Hawk (Great Friend)
- "Are you crazy?! What are we going to do?" - When Knuckles comes up with plan, for Sonic to go Super but Sonic tells him he doesn't have any of the Chaos Emeralds, to which a smug Sonic replies after Knuckles yells at him "I guess we're gonna have to find them again."
- "One day, they love us because we're unique and the next day, we're in jail because we're different." - Knuckles' reaction to the thought of the government imprisoning the animals from Parallel Earth.
- "You messed up my face and now I'm gonna return the favor!" - Knuckles to the Chaotix after they prank him in the matchmaking mission.
- "I'm always the fall guy." - Knuckles after Rouge slips on a rock, knocking him and Sonic on the ground.
- Knuckles uses the third most amount of Engrish in the Japanese version. Coming in right behind Eggman, who uses the second most amount of English, and Sonic himself, who uses English at least once in practically every episode.
- In some scenes of Sonic X, Knuckles' mittens are drawn as gloves.
- In episode 65, Vector says "When I'm through with him [Knuckles], even his own mama won't notice him." Vector is probably mentioning Knuckles having a mother, thus making him possibly the second character (after Cream) to have any parents mentioned in the show.