From Halopedia, the Halo wiki
Rates were a set of formally defined caste-like social strata in Forerunner society, further determined by physical alteration carried out on individuals to suit their societal role. Each rate specialized in a particular field of work, and had varying societal function and cultural importance. Rates were divided into several tiers, including forms, guilds and Maniples.
Adolescent Forerunners, known as Manipulars, were not associated with any particular rate. However, upon maturing, each individual Forerunner would be assigned to a rate, mostly in accordance with the rate of their parents. For example, Bornstellar Makes Eternal Lasting was expected to become a Builder like his father.
The rates were arranged in a certain hierarchy. This order changed to some extent over the millions of years the Forerunner were in power; for example, the Warriors stood at the top in the early days of Forerunner civilization, ten million years before the firing of the Halo Array.
List of rates
The Builders were responsible for the design and construction of most Forerunner technology and architecture, including their weapons, ships and megastructures, most notably the Halo Array. The Builders stood highest in the Forerunner social hierarchy and held immense wealth and political power, with their position consolidating even further after Master Builder Faber and his allies gained control of the Ecumene Council for over a thousand years.
The Miners were a rate responsible for obtaining the materials required for the work of the Builders, as well as stellar and planetary engineering. Miner stellar engineers were colloquially known as plasma jockeys.
The Lifeworkers were a rate specializing in biology and medicine, and the experimentation of various forms of life. The head of the Lifeworker rate was known as the Lifeshaper; the Librarian was the most well-known Forerunner to hold this title.
The Juridicals were the rate charged with judicial matters, including the investigation of crimes and the judgment of criminals within Forerunner society. The Juridical rate was home to Catalog, a collective of evidence-gathering agents. The head of the Juridical rate was known as the Master Juridical.
The Warrior-Servants were the second-lowest rate and primary military caste in Forerunner society. They were responsible for, among other things, the Forerunner victory over ancient humans during the human-Forerunner wars. The Prometheans were an elite group of Warrior-Servants led by the Didact.
The Theoreticals were a rate that existed over one million years before the Didact was sealed in his Cryptum. After one Theoretical named Boundless persisted in studying a certain star in the Spider nebula of Path Kethona despite Warrior orders, she was eventually punished by the Juridicals and sealed within a faulty Cryptum that caused her death. The entire Theoretical rate was then forcibly merged with the Builder rate.
List of appearances