Family of Blood

The Family of Blood was a family 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 consisted of a father (Father of Mine), mother (Mother of Mine), son (Son of Mine) and daughter (Daughter of Mine). While in Human form, the Family could telepathically communicate with each other from a distance. They always referred to each other by their relationship followed by "of Mine", i.e. Father of Mine, Mother of Mine, Son (or Brother) of Mine and Daughter (or Sister) of Mine. Father of Mine and Mother of Mine would obviously have referred to each other as Wife of Mine and Husband of Mine respectively, but this is not seen on-screen.

They also had incredible sense of smell, tracking The Doctor whereever the TARDIS took him by his scent. They also had access to their Hosts' memories, though they had some difficulty pretending to be Humans. (DW: Human Nature / The Family of Blood)

With the similarities in the colour of light they produce, their capability of travelling through the air and the ability to possess cadavers is similar to that of the Rutan Host.

Technology
The Family utilised a spacecraft, that held their 'essence' within it prior to them assuming human form. The interior contained green lights, pillars and paddle-like switches (somewhat similar to the Doctor's TARDIS) and seaweed-like plants dangling from the ceiling. The spacecraft had a considerable arsenal of technology - the most notable of which was a Vortex Manipulator (stolen from the Time Agents) that allowed the craft to travel through time. It could also project force fields, render itself invisible and had bomb-shooting cannons.

On hand, the Family of Blood used energy weapons that fired green energy that disintegrated humanoid tissue - the weapons apparently consist of a living creature within a shell that shot the beam when pierced by the trigger. They were somewhat difficult for humanoids to hold.

The Family also had scarecrow-like soldiers created by Son of Mine and placed in 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. (DW: Human Nature / The Family of Blood)

History
The Family encountered the Doctor and Martha Jones in 2007 and chased them throughout time and space with a stolen Time Agent vortex manipulator in order to steal from the Doctor some means of ensuring that they would live a longer lifespan.

The Doctor was forced to turn himself into a Human using the Chameleon Arch in his TARDIS in order to escape them. The Doctor changed himself into John Smith, 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 Timothy Latimer. He fooled the Family by pretending to still be John Smith. He used an olfactory misdirection (said to be like "ventriloquism of the nose") to trick them into thinking that he was still human, and destroyed their spaceship by moving several switches in an act devised to look like a clumsy accident by "John Smith." The Doctor then punished the family by:


 * Trapping the father in an unbreakable chain forged from dwarf star alloy.
 * Sending the mother into the event horizon of a collapsing galaxy, trapping her there for eternity.
 * Trapping the daughter within every mirror, the Doctor would still visit her once a year. (She is said to be the strange movement you see out of the corner of your eye when looking in a reflective surface).
 * Trapping the son, now locked in time, in the body of a scarecrow to watch over the fields of Earth 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 revealed why the Doctor decided to flee rather than fight the Family of Blood - he was showing them mercy, by allowing them the chance to live out their lives rather than killing them. (DW: The Family of Blood)