The Porcupine is a character introduced only during Bambi II.
He's impatient, easily upset and very territorial, he will do everything to protect his home, a fallen trunk, the only bridge to cross a small river. When Bambi tries to cross it, he gets to see how dangerous the porcupine can be. Bambi "uses" him against one of the hunting dogs that, near the end of the movie, was chasing him.
Trivia: His voice actor, Brian Pimental (who also voiced the Groundhog), was the director of ''Bambi II'', and took on roles as either a writer, artist, animator or actor for a number of Disney and non-Disney feature films.