Character profiles
Leonardo - (Blue) The de facto leader of the Turtles, Leonardo is courageous, decisive, and a devoted student of martial arts. As a strict adherent to Bushido, he has a very strong sense of honor and justice. He wears a blue mask and wields a pair of katanas. He is named after Leonardo Da Vinci.
Raphael(Red)- The team's anti-social bad boy, Raphael has an aggressive nature and seldom hesitates to throw the first punch. His personality can be alternately fierce and sarcastic. He resents Leonardo at times because of his position of authority. Raphael wears a red mask and wields a pair of sai. He is named after Raphael Sanzio.
Michelangelo (Orange)- The easy-going and free-spirited Michelangelo provides much of the comic relief. While he loves to relax, this Turtle also has an adventurous and creative side. He wears an orange mask and wields a pair of nunchaku. He is named after Michelangelo Buonarroti. His name was originally spelled "Michaelangelo" because Peter Laird and Kevin Eastman were using a typewriter, and not a computer, and thus did not have a spellchecker.
Donatello (Purple)- The brilliant scientist, inventor, engineer, and technological genius. He is perhaps the least violent Turtle, preferring to use his intellect to solve conflicts. He wears a purple mask and wields the bō staff. He is named after the sculptor Donatello.
Splinter - The Turtles' sensei and adoptive father, Splinter is a mutant rat who learned the ways of ninjutsu from his own master, Hamato Yoshi. In some incarnations, he is Hamato Yoshi. Splinter is a parody of Stick, the man who mentored Daredevil.
April O'Neil - A former lab assistant to the mad scientist Baxter Stockman, April is the plucky human companion of the Turtles. She embarks on many of the Turtles' adventures and aids them by doing the work that the Turtles themselves cannot do in public. During the early height of TMNT popularity, April was depicted as a television news reporter.
Casey Jones - A vigilante who has become one of the Turtles' closest allies, Casey fights crime with an assortment of sporting goods (baseball bats, golf clubs, hockey sticks, cricket bat etc.) while wearing a goalie mask to protect his identity.
Shredder - A villainous ninja master named Oroku Saki who, along with his evil Foot Clan, is the arch-enemy of Splinter and the Turtles. Shredder wears a fearsome suit of armor covered with sharp blades. It has been rumored that Shredder was not intended to be the main villain for the TMNT series, merely just a minor character.
You can find more profiles in Wikipedia.