Family of Blood

The Family of Blood was a group of hunters who followed the Doctor in order to take his near-immortality.

Biology
The Family of Blood were green, gaseous entities that could inhabit and control Human bodies. Before taking human form, the members of the Family of Blood were kept in small, spherical receptacles. They had very short-lifespans, lasting only 3 months. (DW: Human Nature)

The members that were chasing the Doctor were made of a mother, father, son and daughter. While in Human form the Family could telepathically communicate together from a distance. They also had access to the Host's memory, though they had some difficultly pretending to be Humans. (DW: Human Nature / The Family of Blood)

Technology
The Family had a spaceship, with various features and switches as green as the beings themselves. It also had a cloaking device to render it invisible to Humans.

The Family also had scarecrow-like soldiers created by the son and placed into various fields. They were composed of straw, their molecules animated via a scientific process. Even after being shot down, they could still reanimate by the command of the Family. They could have some relation to the Slabs (DW: Human Nature / The Family of Blood)

History
At some point in their their history they encountered the Doctor and Martha Jones and chased them throughout time and space with a stolen Time Agent vortex manipulator for the Time Lord's near-immortality, as they only had short lifespans. The Doctor was forced to turn himself Human using the Chameleon Arch to escape them, and was disguised as a teacher at a boy's school in England in 1913. The Family, landing nearby, activated animated scarecrows to round up humans to use as bodies. (DW: Human Nature)

The Family's quests for immortality ended when the Doctor was returned to his Time Lord state with the help of Martha, school nurse Joan Redfern and the telepathic Timothy Latimer. He fooled the Family with an olfactory misdirection and destroyed their spaceship by moving several switches in an act devised to look like an accident, destroyed the ship. The Doctor then punished the family by:


 * Trapping the father in an unbreakable chain forged in a white dwarf star.
 * Sending the mother into the event horizon of a collapsing galaxy.
 * Trapping the daughter within every mirror (the Doctor would still visit her once a year for some reason).
 * Trapping the son in the body of a scarecrow to watch over the fields as their protector for all eternity.

In a way, their quest for immortality was won, although not in the way they would have liked.

It was also learnt why the Doctor decided to flee rather then fight the Family of Blood - it was an act of mercy. (DW: The Family of Blood)