Agent D is a dog, his first name is unknown. Not much is shown of him but he was seen in "Traffic Cam Caper". He was injured, along with Agent O, by Dennis the Bunny, the rogue agent, and had his right arm/paw in a sling ("No More Bunny Business"). He was also helping Carl with a drawing of Dennis.
Agent D was seen in "Traffic Cam Caper". He was injured, along with Agent O, by Dennis the Bunny, the rogue agent, and had his right arm/paw in a sling ("No More Bunny Business"). He was also helping Carl with a drawing of Dennis. Agent D also appeared in "It's About Time!" sitting in the crowd with his nemesis at the Dr. Feelbetter Show. However, it turned out to be a trap. The agents starts fighting once they're freed. He made a brief cameo appearance in "Phineas and Ferb Christmas Vacation!" at the O.W.C.A Christmas Party.
He returns in episode "Robot Rodeo" where he was sent out to the L.O.V.E.M.U.F.F.I.N competition and Perry free them and destroy the inators and fight with their nemesis. He appears again in "Rollercoaster: The Musical!" dancing with other agents at the end of the episode. He reappears in Phineas and Ferb The Movie: Across the 2nd Dimension. He was seen to ambush a group of Normbots with other agents. They were, however, captured and saved by Perry, who was also saved by Phineas and Ferb and used his inventions to defeat the invasion of Normbots.
Agent D is a light brown dog with a black nose, dark brown-ish ears, sharp white teeth, a short tail, and an even lighter brown stomach. He is usually seen wearing a dark tan fedora with a reddish-brown band.
In different appearances, Agent D is seen wearing different fedoras.
In many appearances, Agent D is seen near Agent O.
Agent D appears in the online game Robot Riot! as a playable character.
According to his secret file, he specializes in tracking, has instinctive chasing skills, loves group sing-alongs, occasionally scratches behind ears, and pants in hot weather. (Where's My Perry?)
The image gallery for Agent D (dog) may be viewed here.