Zaterra was home to Reptile's race of Saurians who originated from Earthrealm long before it was annexed by Outworld through ten consecutive victories in Mortal Kombat. It used to be ruled by a matriarch. Her influence on the other members of the Saurian race is so strong that over time they begin to revert back to a more primitive consciousness the longer they are separated from her presence, which also affects their ability to maintain a humanoid appearance. In Mortal Kombat: Conquest, however, a former soldier of Reptile says that Zaterra wasn't destroyed because Shao Kahn came to the realization that the Saurians would make wonderful allies in his plans.
In the television series Mortal Kombat: Conquest, Zaterra is depicted as very rainy; thunder can be heard along with the drenching rain, and many transparent Saurians crawl along the limbs of the trees, broken statues and ancient ruins within that realm.
It is unclear when Zaterra was conquered by Outworld, but Nitara's vampire people kept records of their existence before they were annexed by Outworld as well. The known Saurians also seem to retain no memories of their home world, which suggests that the conquest of Zaterra happened in a distant past. Though the Saurian people inhabited the realm prior to being conquered, their first home was Earthrealm which they were forced to leave during the catastrophic battles between Shinnok and Raiden.
A picture in Mortal Kombat: Deadly Alliance's krypt shows the three forms of Reptile in a very swampy area with a primitive-looking house built out of stone or possibly bone, indicating what the world may look like and that it has a clearly primitive technological level.
Because Zaterra is technically still a part of Outworld, it does not have any notable residents, but Reptile and Khameleon could qualify as Zaterrans since they belong to the Saurian race. It's also speculated that the Vampire race also hails from Zaterra, due to their apparently vast amount of knowledge about the Saurians, although this would pose an issue with Nitara's ending in Mortal Kombat Deadly Alliance, which has been shown to have, at least, partially occurred. It is also speculated that Chameleon hails from here. Kiri and Ankha are also two Saurians whom appeared in the series Mortal Kombat Conquest, while another Saurian named Komodai appeared in the cartoon series Mortal Kombat Defenders of the Realm.