Rate

The Forerunner caste system was a system used to rank Forerunners in society. Castes were divided into several tiers, including forms, rates, and Maniples.

Practices
Adolescent Forerunners, known as Manipulars, were not associated with any particular caste. 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.

Each rate had their own ceremonial headgear, worn only on special occasions. However, on a certain day in the Grand Star Season, every Forerunner wore the same style.

Builders
The Builders were responsible for the construction of a majority of Forerunner architecture. As such, they were most likely responsible for creating the Halo Array and Onyx. The father of Bornstellar was a Builder.
 * Master Builder

Miners
The Miners were the second-highest rate in Forerunner society. They were responsible for obtaining the materials required for the work of the Builders.

Lifeworkers
The Lifeworkers were the third-highest rate in Forerunner society. They specialized in biology and medicine, especially with the experimentation of various forms of life. It was not uncommon for Lifeworkers to receive their own planets for experimentation. The Librarian was a Lifeworker.
 * Lifeshaper

Warrior-Servants
The Warrior-Servants were the fourth-highest rate and primary military caste in Forerunner society.They were responsible for, among other things, piloting War Sphinxes during the Human-Forerunner War. The Prometheans were an elite group of Warrior-Servants.
 * Prometheans

Engineers
The Engineers were the lowest rate in Forerunner society, and were presumably tasked with constructing and maintaining structures and machinery.
 * Plasma jockeys

List of appearances

 * Halo: Cryptum