Complex sentence: Prank was once known as Donnie, a classmate of Barbara Gordon (A.K.A. Batgirl) who was unhappy that people didn't appreciate his unsophisticated jokes and pranks.
Split into simpler sentences: Prank was once known as Donnie, a prankster and a classmate of Barbara Gordon, A.K.A. Batgirl. He was unhappy that people didn't like his jokes and pranks.