Harvester (Wednesdays For Beginners)

The Harvesters were an ancient race of scavengers who scoured time and space for people considered special. Able to interface with the dimension of N-Space for a brief time, they could isolate a location in a reality bubble outside of the real universe and scan for their target, phasing out anything the didn't need. (AUDIO: Wednesdays For Beginners)

History
On one Wednesday in 2007, the Harvesters began to isolate Jackie Tyler from N-Space. Their intention was that she would ultimately resort to calling Rose Tyler, which would bring the Tenth Doctor to them, giving them the last two time travellers in the universe. This plot was stumbled upon by Jack Harkness as he was observing the Powell Estate. Though Jackie eventually did call Rose, she realised her error and, addressing the Doctor, insisted that he leave before the TARDIS materialised, robbing the Harvesters of their opportunity. (AUDIO: Wednesdays For Beginners)

Travelling back to his past, Jack shared word of the Harvesters to himself when he was still a Time Agent by the name Javic Piotr Thane. In a plan they concocted together, the Harvesters were lured to the bubble universe where the Council that controlled the Time Agency lived in seclusion. Jack then left the Council and their puppet leader Maglin Shank at the mercy of the Harvesters. (AUDIO: Month 25)