The Book of Ending first appeared in Vertigo Comics, the adult-only imprint by DC Comics in the 3rd issue of the 1st volume of the Trenchcoat Brigade in 1999.
The Book of Ending (aka, the Book of Beginning) is an eldritch book which in the mid-17th century was possessed by the Leshy a people in Ukraine. Whose city was protected by the "Eye of the World" which hide them from the world. Princess Elliana was betrayed by her Cossack lover who snuck into the castle, killed her father, stole the Eye of the World, and led the Cossacks against her city. Slaughtering and enslaving its inhabitants, scattering the survivors across the land.
Seeking revenge she took the book and over the centuries was kept alive and young by M'nagalah, who through her warped eldritch hand influenced her. At the turn of the 20th century, she started to bring M'Nagalah to Earth. The Trenchcoat Brigade having seen a future where all life on Earth had been consumed by M'Nagalah arrived and slowed its entry to the world. Realizing that she was being used by M'Nagalah she changed her mind, thereby helping to prevent his return.