Agent G is a goat agent working for the O.W.C.A. under an unknown division. During the chaos at O.W.C.A. headquarters after Major Monogram had got fired, it was eating memos until instructed by Major-in-Charge Carl to "Quit eating those memos and get out into the field. ("Phineas and Ferb Save Summer")
In "Night of the Living Pharmacists", Agent G is one of the known O.W.C.A. agents that were transformed into pharmacists by the Repulse-inator.