Role in the series
Knuckles is independent, wild, tough and a loner by nature. Like how Sonic embodies the wind, Knuckles embodies the mountain; stern, unmovable and anchored to his duty. Due to having lived in seclusion for most of his life, Knuckles is a rather antisocial and reclusive individual. As such, he cares very little about what others thinks, which makes him bluntly honest, straight-forward and somewhat egotistical.
Knuckles is fiercely loyal to his homeland, and does whatever is in his power to protect it. He prefers to stay close to the island's current emerald shrine to keep a watchful eye over everything on his home. Despite this devotion, Knuckles is willing to leave his duty whenever his help is needed, or when he feels the Master Emerald and Angel Island will be safe. Though Knuckles has found other lifestyles appealing, he will never trade away his duties as he is far too devoted to his role as guardian. When not performing his duties, Knuckles prefers spending his time practicing his fighting skills, going treasure hunting or hang out with his friends.
Knuckles is normally very serious, stoic, collected and usually likes to be by himself. He is likewise stubborn, headstrong and inflexible, prefering to do things his own way, which causes him to clash with others. Regardless, he is very strong-willed, seldom wavering in his determination and will not give up on his goals once he has set them. While he is cool and determined in battle, Knuckles has an extremely short and wild temper and is difficult to reason with when he is angry. Though his temper has often been known to get him into trouble, Knuckles has also learned to use it to his advantage by channeling it into his fighting skills.
Despite being a silent loner, Knuckles is heroic, brave, kind-hearted and selfless, risking his life to save anyone or get them out of trouble, and shows empathy for people, even if they are a villain or enemy. He is likewise a loyal and caring friend, who is always willing to help his friends out in tight situations and will do anything to protect them. When not angered, Knuckles is pretty laid-back and never cracks under pressure. He can also be very understanding on the sly, and doesn't take kindly to people who disrespect or hurt his friends, or innocents in any way.
Having been living much of his life in isolation, Knuckles grew up believing in honesty, and holds a strong and steadfast belief that there is good in everyone, which always lets him give people second chances. Because of his lack of social ingenuity, however, it makes him very naive, extremely gullible, fast about forgiving people and easily misled, which has given him a history of being tricked by Eggman. This has made Knuckles aggressive and suspicious towards anyone he deems questionable. Over time, however, Knuckles has gotten better about this and is more suspicious concerning Eggman's trickery. Once he finds out he has been tricked, Knuckles can get quite angered, but quickly regains enough of his composure to immediately start working towards a resolution.
Though not dull-witted, Knuckles is often prone to rash and ill-advised actions. While not above picking complex strategies, Knuckles often chooses force to be the solution, pushing himself through obstacles while focusing on his goal and ignoring other factors along the way. When in his right element on composed, however, Knuckles can be quite clever, sharp-witted and sneaky, such as setting several successful traps for Sonic and Tails on Angel Island when they first arrived.
Knuckles is said to be shy around women, which makes him act awkwardly around girls like Amy, Blaze and Rouge. Because of his secluded lifestyle on Angel Island, Knuckles feels very uncomfortable in industrialized or crowded cities and places, and being around hi-tech objects or gadgets (mostly because he's not inclined).
Knuckles seems to have lighten up somewhat in Sonic Generations. While he still displays some brooding, headstrong and stubborn attitude, he is shown being better to acknowledge his shortcomings and displays more personal restraint and better social interaction.