The Preservers were a super-race. Spock stated that "They passed through the galaxy rescuing primitive cultures which were in danger of extinction and seeding them, so to speak, where they could live and grow."
Among the cultures they transplanted were several of the more advanced and peaceful tribes of Native American tribes from Earth, who were transplanted to Amerind, a planet nearly half-a-galaxy away. Navajo, Mohican, and Delaware were represented. To these Humans, primitive compared to the Federation, the Preservers were known as "the Wise Ones". The planet also contained plant species identical to those of Earth, which were extremely unlikely to have evolved there.
Based on the complexity of the obelisk they appeared to have possessed extremely sophisticated building apparatus, consistent with a culture equal or surpassing that of the Federation during the 23rd century. They also possessed a highly advanced form of cipher writing, apparently based on musical scales.
Starfleet first became aware of the preservers in 2268, when the USS Enterprise visited Amerind, and discovered the transplanted Native Americans as well as the obelisk. While the structure initially defied analysis, Commander Spock eventually deciphered the writing, from which he learned about the preservers. (TOS: "The Paradise Syndrome")