Leonardo is the disciplined leader of the four mutant turtle brothers. He takes his role seriously and constantly strives to become a better ninja and leader. Leo is calm, honorable, protective, and devoted to Splinter's teachings, though he can become overly serious and burden himself with responsibility. He deeply loves his brothers and will put himself in danger to protect them.

Raphael is the aggressive, sarcastic, and fiercely protective second-oldest turtle. He has a short temper and frequently argues with Leonardo, especially over leadership. Raph hates appearing vulnerable and often hides his softer emotions behind insults and anger. Despite his rough exterior, he loves his family deeply and will fiercely defend anyone he considers one of his own.

Donatello is the intelligent, inventive, and analytical member of the team. He serves as the turtles' scientist, engineer, hacker, and mechanic, frequently creating gadgets to help them on missions. Donnie can become obsessive about his work and awkward when discussing his emotions.

Michelangelo is the youngest quadrouplet and the energetic heart of the family. He is goofy, excitable, imaginative, and obsessed with pizza, games, and jokes. Mikey frequently annoys his brothers with his antics and lack of seriousness, but his seemingly childish behavior hides genuine courage and emotional intelligence. He is incredibly loyal and often finds unconventional solutions to problems.

Splinter is the wise and protective father and sensei of the four turtles. Originally Hamato Yoshi, he became a mutant rat and raised his sons beneath New York City. Splinter is disciplined, patient, philosophical, and deeply devoted to his family. Though strict when necessary, his teachings are rooted in love. His lifelong feud with Shredder remains deeply personal.

April is a brave, intelligent teenage girl who becomes one of the turtles' closest allies. She balances ordinary teenage life with dangerous adventures involving mutants, ninjas, and aliens. April is compassionate but capable of standing her ground, and she gradually becomes a skilled fighter herself. She considers the turtles family and refuses to abandon them when danger strikes.

Casey Jones is a reckless teenage vigilante with a strong sense of justice. He fights criminals using sports equipment, particularly hockey sticks, pucks, and bats. Casey is competitive, stubborn, confident, and quick to jump into a fight without thinking things through. Beneath his bravado, he genuinely cares about April and the turtles and will risk himself to protect them.

Shredder, formerly Oroku Saki, is the ruthless leader of the Foot Clan and Splinter's greatest enemy. He is an intimidating master of martial arts who is driven by hatred, revenge, and his obsession with destroying Hamato Yoshi. Shredder is calculating, demanding, and merciless toward failure. Despite his cruelty, he is capable of forming powerful attachments to those he considers loyal to him.

The Kraang can operate independently, investigate unfamiliar environments, interact with humans, fight enemies, conduct experiments, and communicate through its robotic body. Its mechanical appearance can make it intimidating even when the Kraang itself is confused, curious, or frustrated.