Hegemony was a philosophical direction adopted by certain Dark Templar (Nerazim); those who practiced it were known as Hegemons. Though the Khalai society held Dae'Uhl — the Great Stewardship — as one of their primary moral and political values, the Hegemons instead advocated that continual Protoss existence and security could not be ensured by mute observation of foreign species but rather that continued Protoss imperialism was conditional on vigilance and preemptive action on both extrinsic and intrinsic threats.
A schism between hegemony and Dae'Uhl amongst the Protoss were a contributing factor as to why the Dark Templar left Aiur. Many of the origin Nerazim felt themselves the custodians of continual Protoss security, scouring deep space for potential external threats and "absolving" Protoss society free of potential revolutionaries, often by violent means, while the rest of the Protoss were "safe at home" on Aiur. However, because of their preemptive and aggressive nature, many Hegemons were poorly regarded by other Protoss, who perceived them as brutal murderers who should be excommunicated from the Khala, or at best, disillusioned sentinels paranoid for threats that did not exist.
When the Dark Templar were banished from Aiur, many were Hegemons and sought to continue their ceaseless vigil over the remainder of Protoss society, though they were outcasted. However, with the passage of time and the restructuring of the Nerazim into various Tribes, such as the Lenassa and the Zer'atai, Hegemony began to weaken, many Dark Templar becoming disillusioned and harboring little will to safeguard others, instead interested in the survival and prosperity of their own Tribes and practicing more communal forms of governance. Nevertheless, small sects of Hegemons persisted, insisting on the usage of force to suppress potential alien threats and also violent means — intimidation or even slaying — Khalai who were pursuing the Dark Templar or even Nerazim that opposed their reckless violence. The Fist of Ulrezaj was one of these extremist Hegemon sects, and even many Dark Templar came to regard those few that continued to follow Hegemony as violent and irrational murderers. The Tal'darim, another sect of Protoss extremists, also adopted Hegemon beliefs and that violent force must be used to deter aliens from Protoss artifacts, though they themselves were not Nerazim.
By 2504, virtually no Hegemons remained amongst the Dark Templar. This was enforced by the settlement of the Khalai Refugees on the Dark Templar world of Shakuras; the Khalai, already distrustful of the Nerazim, were especially opposed to the Hegemons and their violent pursuit of Protoss dominion. Although few Nerazim were supportive of Hegemon ideals, virtually none openly practiced it, with Protoss leaders such as Artanis were especially fearful that re-emergence of overt Hegemons would shatter the fragile communion he'd fostered between the Nerazim and their Khalai brethren.
By then, the word "Hegemon" referred to various powerful Protoss fighters discontent with the Templar Caste's management of the war effort that were instead repurposed to be decisive assassins, operating beyond the purview of the Zealots and Stalkers to accomplish a variety of "special missions". Though they were out of favor of the ruling Hierarchy, they were understood to be a necessary evil; operating beyond Protoss beliefs and morals to accomplish tasks that other Khalai "couldn't stomach" in order to preserve continued Protoss security. Due to their relative obscurity and distance from the Hierarchy, they were used for various attacks against Terran Dominion forces encroaching on Protoss space and against rebellious factions such as the Tal'darim and the Fist of Ulrezaj. Though the Protoss never admitted to the slaughter of Terrans or fellow Protoss, the Hegemons served as the clandestine hands of the collective Protoss will, dispensing with various loose ends. Such assassins that were members of the present Hegemons were largely Dark Templar, though few were extremely powerful High templar who had been outcast due to fears of their extraordinary powers or else due to atrocities that they had inadvertently committed against their fellow Protoss.