The Zanans come from the planet Zana, the exact location of which is unknown. Zanans are peaceful, and there has not been any weapon on their planet for thousands of years.
Arriving in 1928, a group of Zanans were trapped on an island, and have no immune defense against bacterias and viruses causing diseases on Earth. They protect themselves with an impenetrable force field which also renders the island invisible from a distance.
They were first encountered by Dr. Walter Jensen in 1958. Twenty years later, Steve Austin arrived on the island inhabited by the Zanans.