Knuckles is described as a "punch-first-and-keep-punching-until-you-need-a-punch-break" kind of echidna, and the best solution to a problem for him is to smash it to pieces. He is determined and strong of character, but tends to be rather cocky and get into trouble.

Knuckles has shown on several occasions to have a huge ego: he clearly thinks of himself as his team's leader and most capable member, and fancies himself very heroic. Also, as a result of his self-pride, Knuckles feels great about himself all the time. However, his self-admiration makes him exaggerate his own recollection of his accomplishments and endeavors to the point of absurdity, leaving him convinced in his mind that he, for example, has various ridiculous superpowers. Proud of his manliness, Knuckles has a very macho-orientated attitude which at times makes him sound somewhat archaic. He is also very blunt when expressing his opinions, which makes him come off as insensitive.

Despite his tough personality, Knuckles is a softy on the inside with some noticeable preferences in particular: he loves nature and is very loyal to his friends. He can also be protective and even gentle as displayed by his dedication to the Fregosi Sapphire and Ms. Tomatopotamus. Also, after reevaluating his status as the last of his kind, Knuckles began feeling the kind of loneliness that comes from knowing that you have no relatives, making him both vulnerable and long for the love only a family can provide. However, he has since come to realize that his friends are his family and that their love is just as good.

Knuckles is the opposite of Sonic: he is stubborn, likes to take his time and is very naive. He is likewise far from intelligent, having admitted himself that he is "as dumb as a rock." Having trouble keeping even the simplest facts on his friends straight, he is a little slow on the uptake, particularly when it comes to elaborate plans and math problems, as even simplified explanations takes him a long time to process. He is also a bit goofy at times and easily distracted to the point where he is drawn to things as simple as shiny objects. Knuckles is not entirely dim-witted, however, having on a few occasions shown some surprising insight, cunning, witticism, sarcasm, and even resourcefulness in different situations. Sometimes he can even tell when he is in over his head. His simple-minded view on things likewise lets him find answers to questions that would otherwise confuse more intellectual individuals. Knuckles can also be quite the charismatic rallier, as he has the grounded and simple (if not selfish) ideals that the common man find very relatable; most noticeably, he was able to convince the villagers of Hedgehog Village to help Team Sonic fight an army of robots by inspiring them to protect their possessions.

Knuckles is a little sensitive when it comes to his intelligence. While he accepts he is not the smartest, he takes great offense when being called stupid and will go to extreme lengths to prove otherwise. Also, when Knuckles got his team into trouble with a half-baked plan, he sunk into a depression over his imposed stupidity until his friends restored his confidence.

Noticeably, Knuckles also has a habit of saying "not cool" to others when they do something he disagrees with. He also has feelings for Amy, but never addresses them externally.

Knuckles is voiced by Travis Willingham, example of his voice can be found here: https://youtu.be/c_qp2mg94EY?t=47