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- Bernardo de la Paz (Prof) – The Moon Is a Harsh Mistress
- Patty Paiwonski – Stranger in a Strange Land
- Penny – Double Star
- Petronius The Arbiter a.k.a. Pete (cat) – The Door into Summer
- Peewee – Have Space Suit—Will Travel
- Longcourt Phyllis – Beyond This Horizon
- Hugo Pinero – Life-Line
- Pixel (cat) – The Cat Who Walks Through Walls, To Sail Beyond the Sunset
- Ponse, The Lord Protector – Farnham's Freehold
- Pug – Glory Road
Read more about this topic: List Of Robert A. Heinlein Characters