The Khthon are a race of small, hairless humanoids introduced in The Pit. They are native to Trieste and look perpetually old and wrinkled. They have the ability to read the mind of creatures, but strong-minded individuals can block against it. They also have the ability to tell the future. The Khthon also knew about the Yssgaroth, which they called the Old Ones.
The Khthon were originally the oppressed minority when the Seven Planets first settled. Though they used to to have a primitive society, they taken by the humans and maltreated. When the Seven Planets became independent in 2396, the Khthons were given more rights but were still the lower class. They were presumably all killed when the Seven Planets were destroyed.