Knuckles the Echidna

"Born and raised on Angel Island, he is the guardian of the Master Emerald. He excels at mid-air gliding and climbing."

- Sonic Mania's description manual.

Knuckles the Echidna is the tritagonist and an anthropomorphic echidna named after his incredible combat using his knuckles. He mostly keeps a serious tone, especially when it's about guarding the enormous gem called the Master Emerald.

Sonic Mania
In the videogame, Knuckles relaxes on the island after the duo Sonic and Tails saved it. After calmly guarding the emerald, he hears noises coming out the place. Five Egg-Robos hunted for another gem, called the Phantom Ruby. Knuckles prepares for a brawl, but ultimately gets knocked down himself. The gem activates and transports Knuckles, including Sonic and Tails, to Green Hill. So have the Egg-Robos, now transformed into the Hard Boiled Heavies. Knuckles and the duo now have to beat down the team.

After defeating Robotnik in his Death Egg Robot, he and his friends see the same villain taking the Phantom Ruby from the Heavies. Once taking said stone, Robotnik, Knuckles and the rest transport to the Chemical Plant. Although traveled into another zone, Knuckles and his friends go forward to defeat Robotnik and his transformed Egg-Robo army. Later, the Heavy King tries to snatch the Master Emerald. Knuckles stops this and returns to his quest along with Sonic and Tails.

Moments later, Knuckles and his friends discover Robotnik's plan to restore a mechanized Little Planet with the Phantom Ruby's power. At said location, Robotnik and the Heavies reside their base of operations there in the Titanic Monarch zone. Making their way to brawl the Eggman and destroying the Titanic Monarch, Knuckles and Tails flee the planet. Sonic and his foe get transported to another dimension. The planet gets freed from it's chain and unveils a star constellation of Sonic in the air whilst the planet vanishes, putting a smile on both Knuckles and Tails' faces.

Sonic Mania Plus
Sonic makes his return after last time and teams up with his friend Knuckles again along side Tails, Mighty and Ray on another adventure to keep the Hard Boiled Heavies away from the Phantom Ruby once again.

After defeating Eggman (now swallowed in a black hole) and the upgraded versions of the Heavies (the Phantom Heavies), Knuckles and the group enjoy their time at an ice cream parlor, but didn't expect the Heavy King to attack them once again with a giant sundae.

Sonic And Tails
Robotnik receives footage from a spy cam, controlled by a Monkey Dude, that zooms in on Knuckles himself carrying around the Master Emerald. Robotnik rises up from excitement and takes Tails' jet to steal it.

& Knuckles
Knuckles arrives deep in the forests of Angel Island and places the Master Emerald next to him, but then hears a sound amongst the bushes. In a thought bubble, Knuckles thinks of three options including Robotnik, the Heavy King, or maybe even Sonic to steal the emerald. He panics and clings onto the gem. He jumps up to grab leaves from palm trees to camouflage the jewel. He hears said noise again and guards the emerald more. The maker of all that racket lands in front of Knuckles, revealing itself to be Ray the Flying Squirrel. Ray tries to shake a hand with him, Knuckles denies. The squirrel then shows a picture of Mighty, who is reported to be missing. Knuckles nods a confused no and sees Ray getting uncomfortably close to the emerald. Knuckles angrily throws him away.

He continues guarding the emerald and sees three Rhinobots, heading for Knuckles. Knuckles cracks his, well, knuckles, and begins to brutally fights off all three. After finishing, he notices the emerald has vanished. He looks under a rock and then looks up to see a shadowy figure riding the Tornado and carrying the Master Emerald behind it. Knuckles assumes it to be Sonic and his companion, leading him to angrily follow the plane.

Mighty And Ray
Knuckles is seen jumping from a cliff, angrily pursuing Dr. Robotnik, who hides in his lab waiting for all heroes to come.

Metal Mayhem
After Sonic and the team "defeated" Sonic's duplicate, Metal Sonic, said robot obtains the Master Emerald, which appears beneath him. Just about he is to gain enough power to brawl the heroes, Knuckles races in the lab, punching Metal Sonic roughly into the laughing Eggman, carrying back the emerald that belongs to him.

Appearance
Knuckles is a red anthropomorphic echidna with a white crescent emblem on his chest and a pointy tail. He wears white gloves with spiky knuckles on it, but no fingers are visible and has a peach colored muzzle with a pointy black nose and black dotted eyes. He also has seven spines that are similar to dreadlocks and Rastafarian flag colored shoes and gray plates with same colored dots on top of them.

Trivia

 * Knuckles was originally supposed to be similar to Jamaicans, clarifying the dreadlocks and the Rastafarian shoe colors.
 * If he'd speak he was actually supposed to talk in a Jamaican accent.
 * He is an expert in fighting, which is shown when he battles the Rhinobots in various ways and also punches Metal Sonic alongside Eggman to the other side of the island. Mighty the Armadillo is also great in combat.
 * Knuckles is born and raised on Angel Island, indicating he has protected the Master Emerald for almost all his life.