Cetra

The Cetra (セトラ, Setora), also known as the Ancients (古代種, Kodai-shu), are a presumably extinct race mentioned throughout Final Fantasy VII. They look identical to humans but have a unique ability to commune with the Planet and guide the flow of its energy. Ifalna, the biological mother of Aerith, is the only Cetra depicted in the game, although the spiritual manifestation of a Cetra appears at the Temple of the Ancients. Aerith is only half-Cetra because her biological father, Professor Gast, is a human.

Early history
During a flashback, when Sephiroth becomes evil after learning of his origins, he reveals a bit about the Cetra. According to him, the Cetra were an itinerant race from which all humans are descended. After a very long journey, they would stumble upon the Promised Land. At some point in time, the Cetra became humans when they gave up their connection to the Planet in favor of permanent settlements and a relaxed lifestyle.

Even more of the Cetra's past is revealed by Ifalna from video tapes in an abandoned house at Icicle Inn. About 2,000 years prior to the events of Final Fantasy VII, the Cetra were reduced to near extinction by the arrival of the extraterrestrial entity Jenova, who infected the Cetra with a virus that turned them into monsters. The few Cetra who escaped banded together and managed to defeat Jenova, which they sealed underground in the area where it first landed, the Northern Crater.

Many years later, Jenova would be unearthed by a Shinra scientist, Professor Gast, who mistook it for a Cetra. As a result, Shinra formed the Jenova Project with the intention of artificially producing humans with the powers of the Cetra, allowing them to reach the Promised Land and use its abundant supply of mako energy to conquer the Planet.