The Architects

The Architects were a race of advanced aliens that came into contact with the Codex  at some point in their history, and used it both to evolve themselves into a higher form of life and harvest the essence of other races in their efforts to dominate the galaxy.

Entwinement
Not much is known about the Architects' past beyond what Al'cor revealed to Tobias Four; but they discovered the Codex at an unknown time, and allowed it to transform them into the third state of life- entwinement. Entwinement was a state at which all members of a species became one mind and spirit, a massive hivemind consensus. This differed greatly from the other two states, organic life and synthetic life, where everyone is still considedered an individual.

Using their newfound abilities and power granted by the Codex, the Architects quickly set about designing the fold-weapons for intergalactic transportation, and developed the Arks to power them, concentrated balls of the Codex's raw energy. With the power of creation essentially in their control, the Architects began to dominate all corners of the galaxy and bend other races to their will. Any who opposed them were harvested, their ideal traits added to the Architect collective as the rest of their essence was cast off into the void-scape of the Codex; this is the cause for the Fermi Paradox.

Creation of the Amalgamation
Due to their haphazard use of the Codex, all of the harvested races' essence in the void-scape began to combine until it formed one sentient entity the Architects called the Seed. Much like the Architects themselves, it and its Amalgamates were a form of entwined life, though the Seed had the same creationistic-powers of the Architects due to its birth from the Codex itself- to what degree these powers could manifest is uncertain.

After it nearly assimilated all organic matter in the galaxy and pushed the Architects to the brink of extinction, they devised a solution that would allow them to survive as well as retain their dominance over the galaxy- they left behind the Inferno of their race, Al'cor, to guide the Inferno in the future along a certain path, then stored the entirety of their species' collective consciousness in the Codex itself. Hoping that humanity would destroy the Seed for them in the future, the plan was for the Codex to unleash them back into the present when all other forms of entwined life were dead.

Al'cor, however, had developed her own identity and reasoning due to her lengthy separation from the Architect collective, and understood that this was wrong. Averting their return by keeping Tobias from activating the final array needed to initiate the Tempest, the Architects stayed trapped in the Codex, and currently remain as such.