D
- John Ezra Dahlquist (Johnny) – The Long Watch. Referred to (under the name Ezra Dahlquist) in Space Cadet.
- Daniel Boone Davis – The Door into Summer
- Hazel Meade Davis (Sadie Lipschitz) (Gwendolyn Novak) The Cat Who Walks Through Walls
- Manuel Garcia O'Kelly Davis (Mannie) – The Moon Is a Harsh Mistress, The Cat Who Walks Through Walls
- Doctor-Livingston-I-Presume (cat) – Farnham's Freehold
- Matt Dodson – Space Cadet
- Dora (computer) – Time Enough for Love, The Number of the Beast
- Dora Smith (Adorable Dora) (Dorable) – Time Enough for Love
- Dorcas – Stranger in a Strange Land
- Dr. Archibald Douglas – Let There Be Light
Read more about this topic: List Of Robert A. Heinlein Characters