Ahti

Ahti (designated Entity A-001 by the FBC) is a mysterious paranatural entity and the "janitor" of the Oldest House.

Assuming the appearance of an older Finnish man, Ahti appeared without explanation in the Oldest House and has subsequently roamed the building as its cleaner. While being monitored by the Federal Bureau of Control, he performs tasks that seem menial but are vital to the safety of people within, and frequently assists Jesse Faden. His origins and significance have been investigated by the FBC to no avail.