This page contains information regarding Star Trek: Picard, and thus may contain spoilers.
In the story of Ganmadan, these demons were shackled at the beginning of time and were waiting for a call to release them from their bondage. This call came from Seb-Cheneb, who blew the horn of the hellbeast Ganmadan, after the death of her twin sister Seb-Natan. The coming of the ch'khalagu was announced by the sky cracking open. After their arrival, they would destroy worlds and lives in a period known as the Thousand Days of Pain. (PIC: "Et in Arcadia Ego, Part 2")