The Arcturians are an extraterrestrial species known to interact with the human race. Little is known about them, except that they were the first sentient alien species encountered by mankind and that humanity has established some sort of interspecies trade with them. It seems likely that they are basically humanoid in form, as they are sexually compatible (at least in a recreational sense) with humans. Arcturians are also the source of Arcturian Klerhaige, a disease that is communicable to human beings.