Leonardo - "Leo" is a hardworking ninjutsu student, learning how to be an effective leader for his three often unruly brothers. He wears a blue mask and fights with two katana swords called Niten Ryu. He also has a crush on April which his brothers all tease him about.
Donatello - "Donnie" is in charge of the design and manufacture of all of the tools and weapons in the Turtles' arsenal, and he is also a gifted hacker. He wears a purple mask and fights with a rokushakubo which converts to a naginata.
Raphael- "Raph" often lets his impulsiveness get in the way of rational thinking. He wears a red mask and fights with two sai.
Michelangelo - "Mikey" loves video games, skateboarding, pranks and pizza. He wears an orange mask and fights with two nunchakuwhich convert into kusarigama. Though he possesses a child-like innocence, Mikey always brings his best game to a fight.
Splinter - Splinter is the mutant rat leader of the entire family, and serves as a father figure for the Turtles. He once was a pet for a renowned martial artist, Hamato Yoshi in Japan. It was from watching Yoshi that Splinter first learned the art of ninjitsu which he then passes on to the Turtles. Splinter often acts as much as a spiritual guide and counselor to the team as he does their teacher. While he does not wield a traditional Japanese weapon, Splinter carries a cane which he can utilize as a weapon (like a bo staff) with fierce proficiency. Unlike the previous animated series, the Turtles often refer to Splinter as their father, rather than their master.
April O'Neil- The 16 year-old granddaughter of Dr. Kevin O'Neil who likes to play video games and eat pizza. April befriends the Turtles after the Kraane kidnap her and her grandfather. This incarnation of April O'Neil is African American and is depicted with pink hair.
Karai - A rebellious teen member of the Foot Clan and an expert kunoichi who stirs up trouble for the Turtles. She is an adoptive daughter of the Shredder.
Baxter Stockman - A technical genius and the scientist responsible for creating the mousers: a series of mouse-like robots that can eat through practically anything.
Jake Canier/Lizardhead- He is April's old childhood Australian boyfriend and next door neighbour who knew her since she was five, nicknamed Jacky. He is a street biker and secretly a member of the Foot Clan, Jackis ordered to New York with Keith. As Jake previously touched his pet chameleon Hardy, the mutagen transforms him into the lizard-like mutant Lizardhead.
Keith/Maddog- He is a large, hulking bully, powerful but fast and very skilled in martial arts. He is the leader of the Purple Dragons street gang in that series and is the Shredder's right hand man. As Keith was previously bitten by Shredder's pet Rottweiler, the mutagen transforms him into Maddog, a muscular, dog-like mutant with a large spikes on his shoulders, a large hands, acute senses, and super-strength.
Foot Ninjas - The foot soldiers of the Foot Clan.
The Kraane- One of the main antagonists of the series. The Kraane are a race of brain-shaped aliens from Dimension Xthat pilot robotic bodies and are responsible for bringing mutagen to Earth. The Kraane have mastered English and communicate in redundant speech.
Scarjack/Metal Klawz- A crabby thug that secretly works with the Kraane. He is exposed to the mutagen in the Kraane's experiments that turned by Scarjack into a giant armadillo-like monster, which he dubs himself "Metal Klawz".
Nick/Killer Bee- A grouchy middle-aged New Yorker who videotapes the Turtles on his cellphone during a rooftop battle with the Kraane. When Nick attempts to sell his video to the Kraane, they kidnap him. The Turtles attempt to rescue Nick, who is splashed with mutagen shortly after coming into contact with a bee. He transforms into a giant bee-like monster, which Michelangelo dubs "Killer Bee". Killer Bee blames the Turtles for his mutation, and attacks them with his sting and acidic spit. During the battle, his cellphone is destroyed.
Dun/Hallocat- A thug working for the Kraane as their getaway driver. The Turtles interrogate him and find out where the Kraane are holding April and Kevin O'Neil. During their mission to rescue the O'Neils, the Turtles crash a truck full of mutagen into the Kraane. Dun is exposed to the the mutagen shortly after coming into contact with a black cat. He transforms into a cat-like monster, which Michelangelo dubs "Hallocat".
Traag- Traag is a lava-spewing, rock monster in service to the Kraane. The Kraane bring the giant through a portal that connects TCRI to Dimension X. Traag proves a challenge to the Turtles, but Zog ends up dragging Traag through the portal back to Dimension X.
Kevin O'Neil - A scientist and the grandfather of April O'Neil. He and April were captured by the Kraane. Although April was rescued by the Turtles, the Kraane made off with Kevin.
Pedro - A parrot that was mutated by the Kraane. Pedro learned to talk and befriended Kevin O'Neil who used him to send a message to his granddaughter.
Leatherhead - An alligator that was originally owned by a young boy and his mother until his father found out and flushed him down the sewer. The Kraane took him to their dimension, mutated him, and experimented on him. He befriended Kevin O'Neil who used him to find his granddaughter. Leatherhead eventually escapes from the Kraane, steals the energy source that powers the portal between the Kraane dimension and Earth, and retreats to the sewers. The Kraane locate and attack Leatherhead, to demand the return of the power cell. The Turtles witness this event and Michelangelo urges his brothers to help intervene. The Turtles protect Leatherhead, restore his health, and keep the power cell from the Kraane.