Blathereen family

The Blathereen were a family of Raxacoricofallapatorians. They were descendants of the Plom family and the Huspick Degenerate. They were in competition with their cousins the Slitheen family and had gained an advantage by 2500. (TV: The Gift, PROSE: The Monsters Inside)

The Blathereens could grow to approximately 8 feet tall. Their large eyes made them capable of improved vision in the blizzards of Raxacoricofallapatorius. Their arms helped them to swim through the oceans. (WC: )

Blathereen seen in 2501 had grey-green skin. (PROSE: The Monsters Inside) The Slitheen-Blathereen and Hanazeen-Blathereen, however, had orange skin. (TV: The Gift, PROSE: A Comedy of Terrors)

Early history
The Blathereen family was once a major family on Raxacoricofallapatorius, until the rise of the Slitheen family. They were generally benevolent and content with middle management, though the Slitheen-Blathereen offshoot considered them weak and feeble. They were also known for hunting down the Slitheen criminals. (TV: The Gift)

Some Blathereen mingled with the Slitheen and the Hanazeen, respectively creating the Slitheen-Blathereen (TV: The Gift) and Hanazeen-Blathereen. (PROSE: A Comedy of Terrors)

21st century
In Glune Fex Fize Sharlaveer-Slam Slitheen's plan to strip Sol of its energy, one of his priorities afterwards was to defeat the Blathereen. (TV: Revenge of the Slitheen)

In 2008 Bloorm Vungah Bart Slitheen, Dax Fex Fize Slitheen and Korst Gogg Thek Lutiven-Day Slitheen stole a technology from the Blathereen that made them able to use skin suits from slim humans. (PROSE: The Lost Boy)

26th century
By 2501, some or all of the Blathereen had become a criminal family. They were controlled by Don Arco and there were enough criminal Blathereen to replace most of the government of Justicia.

They had been trying to create a massive warp-hole to move the entire Justicia system. The plan was to warp Justicia into other solar systems. With the compression technology used in their disguises, they planned to use Justicia's sun as a massive flamethrower. They would destroy planets and use the remains as nuclear fuel (using a similar plan as the Slitheen family used in 2006 but on a larger scale). The prisoners already in Justicia would be used to process the fuel. They were defeated by the remaining Slitheen and the Ninth Doctor. (PROSE: The Monsters Inside)

Named

 * Don Arco Blathereen was the leader of the Blathereen family in 2501. (PROSE: The Monsters Inside)
 * Ermenshrew Blathereen posed as Consul Issabel. (PROSE: The Monsters Inside)
 * Clem Sel Hetch Blathereen worked with Don Arco. (PROSE: The Monsters Inside)

Unnamed

 * Two Blathereen posed as The Governor and Warder Blanc. Both were killed in a prison riot. (PROSE: The Monsters Inside)
 * Many Blathereen worked in Don Arco's plan, replacing the human executives on Justicia, some also acted as technicians working on the Warp-Holes. Most of the Blathereen were killed by rioting prisoners in Justicia and the rest were killed when the Blathereen mothership was destroyed. (PROSE: The Monsters Inside)

Behind the scenes
According to the non-narrative Slitheen-themed edition of Doctor Who Files, the Blathereen family was involved in criminal dealings in the past, but they hid this as to not be exiled like the Slitheen.