History of Praetorian

Overview

The Praetorian is an elite Vex enemy, described by Destinypedia as a deadlier, more aggressive variant of the Minotaur charged with protecting the Vault. It wields a Void-damage torch hammer, has a reinforced Void shield, and can teleport and enter a berserker rage.

Where it matters

Praetorians appear in the Vault of Glass Raid, where they spawn to defend and reset Sync Plates from non-Vex forces. In Destiny 2 they spawn with an Immune Shield that only the Aegis can break, so the Aegis holder must remove the shield before the team can damage them.

Gatekeeper encounter

In the Gatekeeper fight (the penultimate encounter), a shielded Praetorian or a Wyvern spawns in a portal; the Aegis player breaks the shield and passes the Aegis on. The challenge-mode objective requires killing Wyverns and Praetorians within three seconds of each other (per the Shacknews-linked summaries).

Trivia

Praetorians also appeared in the original Destiny and in the Gambit-era "Wolves' Gambit" mission, according to Destinypedia.