Danny McDonough is a character who appears in the 2003 animated series. He is the leader of a group of youths who the neighborhood calls the "wolf pack". They are bullies who terrorize the other children in the neighborhood and are often found playing street hockey.
While visiting April O'Neil at her apartment, the Turtles tell her a story from when they were just tots and decided that they could teach a neighborhood kid how to defend himself. They never realized that the kid, who along with his best friend Stevie, was actually Casey. The Turtles only knew that the two boys were being beaten up by neighborhood bullies led by a kid named Danny McDonough.
Above ground without Splinter's permission, the Turtle tots hear someone running down the alley where they are playing and they quickly hide under a dumpster. They see one boy (Casey) being chased by a gang of bullies. After watching the "wolf pack" pound on Casey, the Turtles want to help, but can't show themselves. To stop Casey's beating, the Turtles begin throwing trash can lids at the gang. The interruption lasts long enough for Danny's mom to call him in for dinner, which breaks up the attack. It is then that the Turtle tots decide to teach young Casey self-defense.
The Turtles were not altogether successful in teaching young Casey any self-defense techniques, but he did learn from them to stand up for himself and his friend. When Casey saw the bullies picking on Stevie and stealing his books, he becomes so angry that he attacks Danny McDonough and takes him down. Grabbing a hockey stick from one of the bullies, Casey defeats and chases off the rest of the group. Danny is the last of the gang and as he starts to rise from the ground, he sees Casey staring angrily at him. Danny gets to his feet and quickly skates away.