Donatello wears the purple bandana and fight with a bo staff. He uses his brains to get his brothers out of trouble and is always trying to improve things around the lair. He has invented things such as the Battleshell, turtlecoms, turtleblimp,the Shell Cycle, and countless other inventions ( most in the early 80's version didn’t work or blew up).
April O'Neil and Leatherhead the mutant alligator often help Dony with his inventions. Since returning from the future (Fast Froward) he blames himself for the "death" of their father and teacher Master Splinter. Dony is acting a lot like Leonardo when Leo failed to protect his family against the Utrom Shredder ( see the Leonardo article).
