Freddie is Baljeet's pet flying squirrel. He is a very good but new agent. His first mission was assisting Perry in fighting Doofenshmirtz. Doof never learned Freddie's name though. Now Agent F fights his own nemesis Dr. Sup.
So Baljeet got him for a summer school class on like taking care of gliding mammals or something (I never figured it out).
He first appeared in Fanfiction episode Perry Meets Freddie (the flying squirrel)