F.O.W.L. (short for Fiendish Organization for World Larceny) is a terrorist organization (similar to S.P.E.C.T.R.E. from the James Bond novels by Ian Fleming) originally introduced in the DuckTales episode "Double-O-Duck" as the "Foreign Organization for World Larceny".
The High Command - They are the head agents of F.O.W.L. It seems that throughout the entire series they never left their certain area (the area they were was possibly F.O.W.L. HQ). Also, they were aways hidden in the shadows, and their true names were never mentioned during the Darkwing Duck series run at all. The ones that usually talked were the one with a big head and fangs and the one with a hunched back, though not always with the same voices (in "Heavy Mental", the large-headed one is a woman). The one wearing the oversized hat never talked. It also appears that they were anthropomorphic birds. All members of F.O.W.L. are shown to fear them, as they appear to be prone to violently dispose of those who upset them, including Steelbeak's predecessor, who was put through six trash compactors.
Steelbeak - Acting like a 1920's gangster, Steelbeak is a rooster who is the top agent of F.O.W.L. He gets his name from the metal beak he wears in place of his original one which was apparently lost sometime before the events of the show, though it is not revealed how. This trademark beak also serves as a weapon because it can bite through almost anything.
Ammonia Pine - A former cleaning lady who worked at a research lab, Ammonia accidentally inhaled the fumes of an experimental bathroom disinfectant, which had a strange effect on her and turned her into a cleaning-obsessed villain. She was later recruited by F.O.W.L. for their dastardly plans. She hates dirt and is even afraid of it. She has a sister named Ample Grime, also a F.O.W.L. agent.
Ample Grime - Ample is Ammonia's messy, dirt-loving sister. No origin story is given for why she loves messes so much. She hates and fears cleanliness as much as Ammonia hates dirt, which proves to be a problem when the two are required to team up.
Major Synapse - The typical R. Lee Ermey-type military man. He once sent an Eggmen military unit into an active volcano so it could be "captured." He steals S.H.U.S.H.'s Norma Ray, using it to turn his useless hippie underlings into superpowered malcontents. He later used it on himself, turning into a giant head with a giant brain that had major telepathic abilities until his own stupidity caused his underlings Hotshot and Flygirl to be flattened by a cartoon anvil which they are last seen crawling away under. His own superbrain explodes when Darkwing Duck, Launchpad, and Gosalyn overloaded him with questions.
Hotshot - One of Major Synapse's hippie underlings changed by the Norma Ray. He controls both fire and ice.
Flygirl - One of Major Synapse's hippie underlings changed by the Norma Ray. She can move things with her mind and can also fly.
Eggmen - F.O.W.L. foot-soldiers, instantly recognizable by their white, egg-shaped helmets.
Wolfduck - Wolfduck was created solely for the Capcom video game. He does not appear in the TV series or the comic book. Because of this, not much is known about him or his back story. Presumably, he was bitten by another wolfduck at some point in time and goes berserk when transformed.
Black Heron - A chemist turned agent of F.O.W.L. and an old enemy from Agent 22's time as a S.H.U.S.H. agent who returns to exact revenge and get her hands on the recipe for gummiberry juice.