Agent O, is an owl that works for the O.W.C.A.; it is brown in color. Its first name is unknown, not much is shown of it but it was seen in "Traffic Cam Caper". It was injured, along with Agent D by Dennis the Bunny (a rouge agent) and had its left foot in a cast ("No More Bunny Business"). In "Phineas and Ferb Save Summer", it is instructed to find out "Who's who?"
- In most appearances it is seen near Agent D.
- In Where's My Perry? its name is revealed as Agent Owl.
- It has large eyes with keen vision. It has Silent flight, perfect for stealth missions. It prefers night missions; it often naps during daytime hours. And it is an enthusiastic dancer.
- "Traffic Cam Caper" (First appearance)
- "It's About Time!"
- "No More Bunny Business"
- "Phineas and Ferb Christmas Vacation!" (Cameo)
- "Robot Rodeo"
- "Rollercoaster: The Musical!" (Cameo)
- "Backyard Hodge Podge"
- "Phineas and Ferb Save Summer"
- Where's My Perry? (Agent File)