Brute Honor Guards are the replacement of Elites as the protectors of the Hierarchs (Truth and Mercy) along with the rest of the High Council and possibly high ranking officials such as Tartarus as seen when he was protected by four Honor Guards during the final battle with Arbiter. 

They always work in pairs or packs consisting of two or three Honor Guard Brutes and one will go beserk when the other Honor Guards are killed. They are impossible to get headshots on thanks to the great protection of their helmets. They are possibly the equivalent to Elite Ultras/Brute Captains or slightly underneath an Elite Arbiter/Brute Chieftain.