Abaddon's release from the Rift

In 2008, Bilis Manger released Abaddon from the Rift so he could feast on all life. (TV: End of Days)

Origins
After being imprisoned in the Cardiff Space-Time Rift in 1876, (PROSE: The Twilight Streets) the Great Devourer, Abaddon, made contact with Bilis Manger and recruited him as his servant. (TV: End of Days)

Preperations
In order to activate the Rift and open his master, Manger sought to manipulate Torchwood Three, first by trapping Jack Harkness and Toshiko Sato in 1941, (TV: Captain Jack Harkness) and then by building on the temptation of Owen Harper and Ianto Jones wanting to bring back their former lovers, Diane Holmes and Lisa Hallett, respectively, culminating in Owen opening the Rift, freeing Abaddon. (TV: End of Days)

Abaddon's rampage
Bilis' plan now fulfilled, he disappeared, (TV: End of Days) getting tangled up with the Committee and being trapped in Traveller's Halt, (AUDIO: Deadbeat Escape) leaving Torchwood to deal with Abaddon's feast; taking every life his shadow cast over. Drawing him to an open space, Jack allowed Abaddon to feast on his immortal life, gorging him until his death, and leaving Jack seemingly dead as well. (TV: End of Days)

Aftermath
Jack returned to life a few days later, and promptly left (TV: End of Days) after hearing the Doctor's TARDIS landing at Roald Dahl Plass. (TV: Utopia) Jack's disappearance left Torchwood Three temporary disarray. (TV: The Sound of Drums, Kiss Kiss, Bang Bang)