The most ancient and powerful race in Halo. They are classified as a tier 0 Race, being able to create galaxies and cause evolution to occur at much increases rates. Their constructs are created using neural physics which causes them to be completely invulnerable to any form of attack except a very specific type. That type being the Halos. They literally laugh at the concepts of life and death, being able to move in and out of both whenever they choose. They are also able to change their physical form whenever they want. They are older than the universe itself and created both the human race and the forerunner race. They have these giant Star Roads that were used to connect star systems together. Meaning that each one was literally light years in length. These could be used in combat and were capable of crushing straight through stars and planets with ease. They can travel across a multitude of dimensions. Some of them became the flood, which was used to test the humans and precursors, but are way more powerful than both combined. The only way they were defeated is because they allowed themselves to lose. TL;DR: Precursors are basically a race of gods. They are OP as hell.