Humans

Humans were originally from a core world called Terraxia, and lived there for two billion years, where they began to develop interstellar technology. However, as they hadn’t discovered subspace highways, they were unable to go much farther than the core with their light-speed technology. This was the period of time in which first contact between elves and humans was made. Information was shared and subspace highways were discovered. Shortly after first contact with the elvish, their home planet's sun had reached the end of its lifespan. As they had not yet found any habitable planets that didn’t have any form of life above micro-organism living on it (Conservation and Natural Evolution laws, don’t ask), they pooled all of their resources to build a mega-station at the convergence of the two biggest natural subspace highways. They called it Nexus station. While humans have spread far from their original home and can be found in every corner of the galaxy, every one of them can trace their roots back to Nexus Station.

While they might not be the most powerful species, they are definitely the most common, and are also still the ruling power of Nexus, the largest station in the galaxy, which is basically just an artificial planet. Humans are also the most common species in the military, mostly because of their scrappiness, violent tendencies, and general poor decision-making.