Reapers (Earth-1791)

The Reapers, designated as LF.Xx.3273 by the Protheans and referred to as the Parasite by the Covenant, is a species of highly virulent insectoid organisms that reproduce and grow by consuming sentient lifeforms of sufficient biomass and cognitive capability. The Reapers were responsible for consuming most sentient life in the galaxy, including the vast majority of Protheans, during the Prothean-Reaper War in ancient past, prompting the activation of the galaxy-sterilizing Halo Array in 100,000 BCE.

Originating as a corrupted form of the galaxy's most ancient custodians, the (???) the Reapers reproduces and spreads by infecting other organisms, hijacking their bodies and nervous systems in order to transform them into one of many specialized forms. Through infecting sentient lifeforms, the Reapers assimilates their memories and intelligence, and the species becomes collectively more intelligent as a result. Because of their frighteningly rapid growth rate, as long as enough hosts of sufficient biomass and intelligence are available, the Reapers are effectively unstoppable.

All Reaper forms share a single consciousness, which becomes progressively more intelligent and sophisticated with every sentient host that is assimilated. When enough hosts have been infected, the Reaper consciousness becomes a Sarlacc - a self-aware, highly intelligent entity that strategically commands all Reaper forms in an outbreak. Due to this group consciousness, the Reapers as a whole is more accurately described as a single, transsentient macroorganism rather than a collection of individuals directed by one or more controlling beings. In the absence of the Sarlacc, the Reapers possesses only basic coordination; they are incapable of forming complex strategies, and focus solely on attacking and infecting nearby sentient organisms. This stage of a Reaper outbreak is known as the Feral Stage. At this stage, the Reapers seek to create an assembly of biomass, calcium, and nervous system reserves, which leads to the creation of a Reaper hive and the beginnings of a Proto-Sarlacc. The nature of the Sarlacc's collective consciousness has been likened to a socialist utopia, due to the fact that the Reapers act as a unified entity, with no individuality that would be present in other, more traditional species; each component of the Reapers meta-organism works tirelessly for the advancement of their species.

The Reapers presents a highly variable and unconventional threat in combat, as it can infect and mutate dead or captured opponents into a myriad of deadly forms, effectively growing stronger as it weakens enemy forces. They are widely considered to be the greatest threat to the existence of life (or, more accurately, biodiversity) in the Milky Way Galaxy.