The first era in the evolution of the Universe, also called the Early Universe. This era was notable for the unimaginable energy density that permeated it. In less than a second after the Big Bang, the Universe had expanded far enough that the four fundamental forces had fractured, leptons and mesons (2-quark hadrons) had condensed from the energetic particle soup, and the first baryons (3-quark hadrons) were forming. Over the next million years, the soup thinned enough that nuclei of deuterium and helium could form, and electrons could be captured by the nuclei (including lone protons to form protium).
There was no preceding era, and the succeding era was the Stellar Era.