Sisters of Plenitude

The Sisters of Plenitude were the main antagonists of the Doctor Who episode "New Earth" and were of the Catkind species (being, in simple terms, anthropomorphic cats) - despite the order believing itself to be the caretakers of the sick they were in reality a ruthless sect willing to perform unspeakable acts in the name of the "greater good".

History
The Sisters of Plenitude were an order of Catkind nuns, devoted to helping the sick (though they were ready to defend their lives with violence). They worshipped the goddess Santori but not much else is known about their faith.

One group of the Sisters had a hospital on New Earth, outside of New New York. This hospital was created before the humans got there and was created to deal with all their diseases. They had cures for nearly every known ailment and were able to heal their patients with remarkable efficiency. Many of the treatments shouldn't have been discovered for at least a thousand years, according to the Tenth Doctor.

Unfortunately, these amazing skills were gained by using thousands and thousands of grown human clones. They were infected with every known disease and killed if they started to show signs of thought. This was due to the fact that other, more humane methods were too slow to deal with all the diseases. These disease carriers were released by Lady Cassandra and eventually cured by the Tenth Doctor. The Sisters were later arrested by the NNYPD for their actions.