I am not sure you can really know someone by reading about them but I think this is probably as close as you can get to understanding Gaiman without actually knowing and interacting with him in real life.
- The Space Between the Stars by Anne Corlett
- Brandywine: A Military History of the Battle that Lost Philadelphia but Saved America by Michael C. Harris
- If I Understood You, Would I Have This Look on My Face? by Alan Alda
- A New Hope: The Princess, the Scoundrel, and the Farm Boy by Alexandra Bracken
- The Life-Changing Magic of Not Giving a F*ck by Sarah Knight