Donatello and his brothers were once ordinary turtles; when they were infants, they were adopted from a pet store by Hamato Yoshi, Splinter. When their soon to be father walked passed a strange man, a kraangdroid, he felt something odd about him and followed. Unfortunately Splinter gave away his position when he accidentally stepped on a rat's tail. The Kraang found him and attempted to kill him, but Splinter fought back hard. In the end, the Kraang dropped the canister of mutagen causing the turtles and Splinter to mutate. Splinter came in contact with a rat last, thus mutated into a rat, while Donatello and his brothers, after coming in contact with Splinter when he was human , mutated into humanoid turtles. Splinter knew they would never be accepted in society, so he took them to the sewers, made a home down there, and made the four turtles his children. Knowing the world would be dangerous and there would be a time where they want to explore the outside world, Splinter trained the boys in the art of Ninjitsu. Donatello and his brothers were named after great Renaissance artists from a book Splinter fished out of the storm drain.