History of Gatekeeper

Gatekeepers are large Vex enemies fought in the Gatekeepers encounter of the Vault of Glass raid, the penultimate encounter before Atheon.

Overview

The encounter takes place in the Glass Throne and runs in two phases. Teams stand on sync plates to hold open portals to Mars (the past) and Venus (the future), pass a Relic between players, and defend the Conflux from Praetorian sacrifices. Praetorians carry white shields that only Relic damage can break. Players who use a portal get the Teleport Destabilized debuff, and in the portal dimensions players receive Marked by the Void, which the Relic holder must cleanse.

Source disagreement

PCGamesN says there are three Gatekeepers, one each in the past, present and future, killed by a team entering the portals. GameRant describes Gatekeeper Hydras appearing on the central block and closing both portals instantly. Both agree the encounter feeds into the Atheon fight.

Challenge

The encounter challenge is Strangers in Time. Datto's Master Vault of Glass guide covers the Gatekeepers from 13:28.