Vortex Dweller

The Vortex Dwellers were advanced beings who lived in the Time Vortex.

Biology
Vortex Dweller were made of a ooze-like form that constantly changed in colour. They were capable of changing their shape to a degree, which one Vortex Dweller used to try to become more humanoid. Their normal method of communication was with electrical shocks. Due to high voltage (at least 50,000 volts), they were generally unable to communicate with lesser beings. They also produced chronon energy.

Vortex Dwellers were capable of advanced control of space and time. They weren't technically capable of changing time, but they could re-arrange it. For example, the Vortex Dwellers could bring people who had died back to life, though they would still have scars and memories of the deaths. They were also capable of closing time rifts. (TWN: The Undertaker's Gift)

History
Vortex Dwellers lived in the Time Vortex and only came into the normal universe in very rare occasions. Jack Harkness only knew of them by reputation.

In 2009 a young Vortex Dweller came to Cardiff via the Cardiff Rift. It accidentally killed two people before Torchwood was able to bring it to the Hub. As it was unable to communicate with the humans, it simply sat in its cell and waited. In the meantime, its parent started looking for it, but was unable to track it as it was in the normal universe.

When the Undertaker's Gift was activated, it tore open a hole in the Rift. The parent Vortex Dweller was able to detect the event and investigated. Jack Harkness was able to reunite the child and parent Vortex Dwellers. He then tried to communicate with them, killing him repeatedly but successfully getting their help. The Vortex Dweller repaired the damage from the Undertaker's Gift, brought back several people who were killed and stopped the Hokrala Corp from sending anything else into the 21st century. It also offered to seal the Rift, but Jack declined. (TWN: The Undertaker's Gift)