Knuckles is a hunky Mobian short-beaked echidna with a beefy build, red fur and the Nike logo on his chest for unknown reasons. His eyes are porple. He wears a hat sometimes.

Knuckles is stoic, strong, dignified but also naive, gullible and easily manipulated by Eggman.

Despite his rough core, he is afraid of ghosts.

As per his name, Knuckles is exceedingly good at punching things due to his unnatural strength. He often brags about this, claiming to be 1 million percent muscle.

Knuckles was born to a small branch of Echidnas living in the Hidden Palace. When Knuckles was only a child, his clan want out to fight the Owls. They did not win, and thus, Knuckles was the last of his kind. The only Mobian echidna left.

Knuckles had the duty of protecting the Master Emerald whatever the cost, and would fulfil his promise for as long as he lives.

One day, Dr. Eggman travelled to Knuckles' location. Initially, the echidna was suspicious of the strange fat man. Eggman told Knuckles that a blue hedgehog and golden fox were out to destroy the Master Emerald.

(obviously, this is a lie)

Somehow, Knuckles was gullible enough to believe Eggman's lies, and the two teamed up to destroy Sonic.

Eventually, Knuckles realised Eggman was lying and teamed up with Sonic.

And the rest is history...