The Captain-Keeper of The Front Door is the main guardian of the Front Door. During the Series, it is never revealed who the Captain-Keeper Of The Front Door is. Although Arthur wanted to promote the Lieutenant-Keeper of The Front Door, Although it is revealed that is impossible, as the Captain-Keeper Of The Front Door is The Architect.
During the series, the Captain Keeper is often reffered to as being 'lost' for 10,000 years. And until his/her fate is found out, no action can be taken.
- Garth Nix had written somewhere in the book that the Captain-Keeper was The Architect, But his editors removed it.
- In a book-signing, he was asked who the Captain-Keeper was, He revealed it was The Architect.