Cetra

This is not FF7 canon. Well, some of it is. Most of it is not. This is mostly me trying to keep my notes straight. Spoilers abound.

Sometimes called the "Ancients", the Cetra were an ancient race of humans who became extinct due to a mysterious illness and what their texts describe as "the crisis from the skies".

The Cetra left behind an fair bit of archaeological data including, murals, texts, art, temples, and other buildings. Indeed, there is rumored to be an entire city somewhere on the Northern Continent.

Jenova of course was the "crisis from the skies" and the mysterious illness Geostigma.

Aeris Gainsborough is said to be the last of the Ancients. Her mother was Ifalna, her father Faremis Gast. Technically, she is only half-Cetra. What many do not realize is that the ability to communicate with Planet is not dictated by blood. It is an ability that can be learned. Ifalna was trained by her family at an early age, and in turn taught her daughter when she was very young.

While skill levels can vary, pretty much anyone can be taught to listen to the Planet. Learning to speak Cetran, however, is another matter entirely.