Knuckles the Echidna

Knuckles the Echidna (ナックルズ・ザ・エキドゥナ) is an anthropomorphic red echidna from the Sonic the Hedgehog and Sonic Universe series. Knuckles is very strong and somewhat gullible. In his first appearance, he was tricked by Dr. Eggman into thinking that Sonic the Hedgehog was an enemy, but after discovering the truth, he became a friendly rival of Sonic. He is the guardian of the Master Emerald, and prior to Eggman and Dr. Wily's Genesis Wave was the leader of Chaotix.

Worlds Collide
Dr. Wily and Dr. Eggman captured Knuckles and turned him into the Roboticized Master Knuckles Man. His Special Weapon was the Sharp Knuckle. Knuckles Man, alongside Tails Man, Rose Woman, and Shadow Man were sent to Mega Man's world to steal a Chaos Emerald from a bank in Mega City. They were held off by Proto Man and Mega Man, although a blue blur interfered, buying the Roboticized Masters enough time to escape, and likewise resulting in Mega Man being tricked into fighting Sonic the Hedgehog. Knuckles Man and the others then delivered the Emerald to Wily and Eggman in the Skull Egg Zone.

Later, Knuckles Man was one of the Roboticized Masters sent after Proto Man while Vector Man, Charmy Man, and Espio Man fought against Sonic, Mega Man, Rush, and Tails. Knuckles Man, alongside Rose Woman, while watching Proto Man and the restored Chaotix Roboticized Masters (Vector the Crocodile, Charmy Bee, and Espio the Chameleon, respectively), were then ordered to pursue Sonic and Mega Man. The two Roboticized Masters, upon receiving their orders, announced that their self-destruct protocol had been activated. They later encountered Sonic, Tails, and Rush, with their self-destruct protocols remaining active (ironically warping in just as Sonic wished that they warp in and ambush them). Mega Man was barely able to deroboticize them in time with the Sonic Blast.

Knuckles, upon reasserting his identity, was then teased by Sonic about being tricked by Eggman again. Knuckles, upon discovering Wily and Eggman were involved, demanded to know where they were so he could "get a crack on them," with Sonic, to Knuckles' chagrin, teasing that he'll do it "'Cause you're [Knuckles is] tougher than the rest of them? The best of 'em? Tougher than leather?". Sonic then sent Knuckles and Tails to help the Chaotix crack the teleporter password. They were unable to crack the passcode before an entire army of time-cloned Robot Masters (exempting the first generation of Robot Masters), led by Rouge Woman, attacked them at the main base, and fought them. Knuckles proceeded to dodge a Black Wave attack from Rouge Woman, and then fought with Concrete Man and Stone Man, breaking the latter's arm with one punch and tauntingly asking if that was all Stone Man could dish out, and then proceeding to smash the former's Concrete Shot effortlessly. According to Stone Man, Knuckles' strength is comparable to that of Guts Man. He later held the Robot Masters off while Mega Man, Sonic, Tails, and Rush attempted to board the Wily Egg. Knuckles eventually ran into trouble with Knight Man.

By the time Sonic and Mega Man ended up captured, they were worn down by the other Robot Masters, although Knuckles managed to land a punch on Clown Man. He eventually bore witness to Dr. Light's original Robot Master's arrival, although he asked Dr. Light whether he should smash them (enemies) or not smash them (allies), with Light stating they're the latter. Upon the discovery that something might have gone wrong in regards to Sonic and Mega Man, Knuckles proposed that Dr. Light, Proto Man, and himself can infiltrate the Wily Egg to rescue and cover for Sonic and Mega Man with Light destroying the Genesis Wave Generator, while the newly found reinforcements can hold off the Robot Masters. With Elec Man agreeing to the plan, Knuckles then used one of the Item 2s to fly up to the Wily Egg alongside Proto Man and Dr. Light/Rush, although not before telling the injured Tails to "keep his head down."

Knuckles, Proto Man and Dr. Light then rescued Sonic and Mega Man, with Sonic also jokingly telling the former that he'll "never let [Sonic] live this down." Knuckles and Proto Man then proceeded to fight Eggman and Wily while Sonic, Mega Man, and Dr. Light shut down the Genesis Wave Generator, while doing significant damage to the Egg-Wily Machine X (which the doctors were partially at fault for, due to sabotaging each other's defensive systems). However, they eventually are at the doctors' mercy when the Egg-Wily Machine X does a full system reboot via the Chaos Emeralds, with Knuckles also lamenting about failing to let the two doctors steal the Master Emerald as he could have exploited that by having it neutralize the Chaos Emeralds, although Super Sonic and Super Armor Mega Man saved them in the nick of time. The two then departed with Dr. Light, but were enveloped by the Super Genesis Wave.

Aftermath
Due to the changes made to Sonic's world (due to Dr. Eggman interfering with it's restoration), Knuckles was no longer associated with Chaotix, other than as an occasional ally.

In addition, the other Echidnas no longer exist in the present time, leaving Knuckles as the only one. (Sonic Universe #63)

Worlds Unite
By the time of Sigma-1 set out to conquer all worlds, Knuckles had joined forces with Sonic's teammates, the Freedom Fighters, in his search for the fragments of the Master Emerald. He and his allies later traveled to Mobotropolis in an effort to stop M'egga Man, who had attacked the city and attempted to place one of Sigma's Unity Engines. Despite their combined power and the aid of the robot Gemerl, the heroes were unable to stop the corrupted Mega Man, who was eventually cured by the attack of Sonic Man. Though both were restored, their worlds were merged together according to Sigma's plan. As such, Knuckles and the Freedom Fighters joined forces with the Robot Masters, Maverick Hunters, and Team Sticks in order to hunt Sigma down. A brief flight on the Sky Patrol took them to the Lost Hex, where they faced Sigma's defense force: an army of Mechaniloids led by the Deadly Six. Knuckles and his teammates fought bravely, but the tide turned against them when the aliens took control of the Robot Masters, Gemerl, the Maverick Hunters, and Bunnie Rabbot's robotic limbs.

Knuckles was forced to do battle with Break Man, who suggested that his nuclear core might help put a dent in the enemy forces. Following this confrontation, he came to the aid of Sally Acorn before retreating inside the Sky Patrol with the others.

Super Smash Bros. for Nintendo 3DS / Wii U
Knuckles occasionally appears in the background of the Green Hill Zone. Additionally, a Knuckless costume for the Mii Brawler was released as a DLC.