Inhabitants of the Valley Dor, they worshipped the "living goddess" Issus (who is actually merely an ancient Black Martian woman), and sought to keep her happy with human sacrifices. For centuries, they enthusiastically promoted the idea that the Valley Dor is the gateway to Martian Heaven and decreed that any Martian who had reached 1,000 years of age or merely tired of living should travel to the valley to either spend the rest of eternity in paradise or be reborn. When the unsuspecting pilgrims reached the valley, they found a beautiful land where fruit and water were plentiful... which also happened to be heavily inhabited by white apes and plant men. Those who survived those creatures ended up enslaved by the Holy Therns, who would work them to death before feeding them to Issus or the Tenth Circle. The Holy Therns' downfall came in 1886, when John Carter suddenly returned to Mars. Their leader was the Holy Hekkador, and at the time, it was Matai Shang until his death at the treacherous hands of Salensus Oll. After the fall of the Cult of Issus and John Carter became Warlord of Mars, Jagati Khen was named the next Holy Hekkador. However, he would conspire against Carter by transporting another Earthman, Tarzan of the Jungle, to Barsoom and convince him that the Jeddak was a oppressive tyrant, setting one against the other.
Therns resembled Caucasian humans with blue eyes and blonde hair at first glance, but in reality, they are all hairless and wear wigs to cover their heads. They are dressed in revealing jewelry and ornaments like most Martians, but their leaders favor long, loose robes instead.
In Other Media
Therns appeared in the 2012 John Carter movie as the main antagonistic force. In the movie, they are depicted as a extremely advanced alien race not originated from Barsoom that has manipulated the course of history in many worlds. Therns are depicted as far more formidable than their book counterparts, capable of advanced psychic powers, shapeshifting and energy manipulation.