Perry the Platypus

Perry the Platypus (full name) is Phineas and Ferb's pet platypus, who, unknown to his owners, lives a double life as a secret agent. He has a lair under the Fletchers' house that can be entered through a lot of passages, like a tree in the backyard, the "Chimneylator", (an elevator inside the chimney), or many other places that lead to underground tube systems. His nemesis is Dr. Heinz Doofenshmirtz, and he is always sent to foil the doctor's plans, which he always successfully accomplishes. A running gag in the show is that his missions always end up covering evidence of Phineas and Ferb's activities by accident, thus Linda never finds out about the boys' schemes.

Relationships with other characters
 Phineas and Ferb

Perry is Phineas and Ferb's pet platypus. They never learn that he is a secret agent. Whenever Perry leaves for a mission, Phineas asks "Hey, where's Perry?". It is shown that he does care for his them when he learns that Dr. Doofenshmirtz's "Make-Up-Your-Mindinator" will destroy Phineas and Ferb, as he attacks him them handcuffs him to a pipe.

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