The ancient humanoids were one of the oldest sentient species and possibly the first humanoid species to evolve in the Milky Way Galaxy on an ancient planet. They flourished some 4.5 billion years ago and explored the galaxy, but found no other lifeforms like themselves.
Believing that the life span of a single species was finite, the ancient humanoids seeded the primordial environments of many planets with a DNA code that would direct the evolution of life on that planet towards a form similar to their own. At least Earth, Indri VIII, Loren III, Ruah IV, and Vilmor II were directly seeded by the ancient race. Other species that likely originated from seeded primordial seas included Klingons, Romulans/Vulcans, and Cardassians. Some of the fragments of DNA also contained parts of a computer program designed to display a holographic message from an ancient humanoid explaining her race and their actions. It was hoped that their descendant species would come together in the spirit of cooperation in order to assemble the program.
In the 2360s, the noted Federation archaeologist Professor Galen discovered the existence of the program and began collecting the genetic samples. However, the Klingons and Cardassians also learned of the program and sent expeditions of their own to assemble it, each believing it to contain a great technological advance, while the Romulans observed all of them under cloak. After Galen's death in 2369, Captain Jean-Luc Picard of the USS Enterprise-D was able to convince the Klingons and the Cardassians to cooperate with them to finish the program.
The last part of the program was obtained on Vilmor II, and the message was played to the assembled members of each present party. The Klingons and Cardassians rejected the message due to their own prejudices, but the Romulan captain later expressed to Picard in confidence that perhaps their races were not as different as they had previously believed. (TNG: "The Chase")
The ancient humanoid in the recorded message was played by Salome Jens, who later played the Female Changeling on Star Trek: Deep Space Nine. In the final draft of the script, she was described as "a humanoid – in fact, one of the coolest humanoids we've ever seen, with a face wise and tragic and light-hearted all at once."
Ronald D. Moore has stated that he considered, but intentionally did not specify, that this species was the Preservers from TOS: "The Paradise Syndrome". He noted, "but this could be them and be internally consistent." (Star Trek: The Next Generation Companion (2nd ed., p. 244)) It should be noted that the ancient humanoids seeded worlds 4.5 billion years ago, while American Indian cultures like the one saved by the Preservers only emerged in the last 10,000 years. Regardless, Star Trek Online has a storyline that confirms that the two races are the same within the canon of the game.
According to the Star Trek: Star Charts (p. 72) and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the First Humanoids came from the Gamma Quadrant.