Sentinel

Fallout 3
is a rank used by the Capital Wasteland Brotherhood of Steel, ranking between Paladin and Elder. The only Two member's of the Brotherhood to have achieved this rank at the time of Fallout 3 is Sarah Lyons, who leads the Lyons' Pride elite unit. The Lone Wanderer also becomes a Sentinel if you complete Broken Steel by choosing to destroy Adams Air Force base instead of destroying the Citadel.