The Usurians were manipulative life forms native to the planet Usurius.
The Usurians didn't need to breathe and looked like a small handful of green seaweed with eyes in their natural form, although they belonged to the fungus, not vegetable kingdom. They could assume the shape of a dwarfish humanoid as long as they constantly exposed themselves to particle radiation. They were listed in Professor Thripsted's Flora and Fauna of the Universe as poisonous fungi. (TV: The Sun Makers)
They were originally a war-like race, but decided it was inefficient and turned to commerce, creating the Company. Their databases contained information on Gallifrey (which they did not consider a viable market for their consumer products) and knew of the Doctor's acts of "economic subversion". (TV: The Sun Makers)
By the 22nd century, Legion had encountered the Usurian and noted their obsession with business. (PROSE: Lucifer Rising (novel)) The Veltrochni of the 34th century also knew of them and their mania for profits. (PROSE: The Dark Path)
At some time much later, the Company moved humans to Mars after Earth became uninhabitable from pollution. The humans were nearly taxed to death. When Mars also became uninhabitable, they moved the humans to Pluto and set up six artificial suns. They drugged the humans, exploited them and taxed them ruthlessly under the leadership of the Collector. (TV: The Sun Makers)