Like Esmerelda, the Guardian is the only one of his kind in this world. He is a living construct created by Sterran using an ancient and long lost process.
Long ago, before the breaking, the warforged were created for a now forgotten war. At some point, the race of constructs developed their own sense of purpose and sought independence from their creators. Eventually, the peoples of the world came to recognize the warforged as a new and separate race. It can only be assumed that their race became extinct long before the arrival of the dragonborn fleets, and the art of their creation lost in the rubble.
Sterran, in his many travels, rediscovered an ancient creation forge and the secrets of its workings. The guardian is the product of years of study and experimentation. It was only hours before his death that Sterran awakened the Guardian. Because of this, the guardian was only given his most basic instructions; protect Esmerelda. He is intelligent and skilled as a warrior, but he is an infant in his understanding of the world.
Though he is an artificial creation, the Guardian is a living, thinking, and feeling being.
Guardian’s Character Sheet