Sonic has a lot of self-confidence and possesses an enormous ego to match it, making him sassy, quick-witted, cocky, and at times overconfident. No matter the threat, Sonic always remains cool under pressure.[17] In the original Japanese version, Sonic omits honorifics and speaks informally (if not rudely), using "ore" instead of "I" when addressing himself or others ("ore" is a boastful way to say "I" in Japanese). However, he sometimes uses honorifics when addressing close friends or acquaintances. Possessing a narcissistic tongue and big attitude, he often jokes around to light the mood and will also take any opportunity to taunt his opponents. Being so smug, Sonic has developed a habit of talking to mindless robots, even when he knows they cannot hear him. Despite this, he can be quite the gentleman when he wants to and be modest with fancy titles. Also, while Sonic generally assumes that he can deal with things on his own, he also realizes he has friends to back him up in troubled situations, and believes strongly in teamwork. Owing to his smugness and confidence, he often engages in playful banter with his enemies, such as his asking Infinite, as "optional" questions to glean into what the secret behind the latter's powers were, what the latter's favorite color was and whether he liked long romantic walks on the beach, as well as "asking" a Zavok replica if he would let Sonic join a party occurring on the Death Egg (referring to the commotion resulting from the Resistance's infiltration of the area).

Following his free-spirited nature, Sonic never dwells on the past or allows his painful experiences to weight him down. Instead, he lives in the present and always looks forward to his next adventure, holding no regrets for what has transpired. It is only in the moments of greatest loss that his macho and carefree appearance falls away. Sonic is also of incredibly strong character and will: no matter the situation, he never doubts himself or gives up, never once submitting to the darkness in his heart.

Sonic is extremely loyal to his friends and will risk his life for them without any due consideration.[1][21] While he can leave them hanging, act rude towards them, or endanger them due to his fast-paced nature, Sonic never intends to make his friends unhappy and values them above all else, treating each of them as the most important person in his life. Equally, Sonic will always accept help from his friends and show great trust in them, though he is not above making mistrusting assumptions of them.[25]

Regardless of the many foes he has faced, Sonic rarely considers them true enemies, and instead tends to admire them for how powerful some of them are and how much fun they can give to him.[26] Likewise, Sonic is shown to have a remarkable capacity to forgive, forgiving Silver and working with him after he had tried to kill him twice.