Sergeant Erwina Prowley (or Aunt Prowley) was the leader of the rangers.
Erwina, prior to 99942 Apophis impact, was a Green Beret american military. She was onboard Vineland Ark, and after emerging, she founded the Rangers and laed them in the fight against the Authority during the Authority Wars, and it is said that was she the one which gave General Cross for dead. After the war, she married an old Bandits and had a daughter with him, Lily Prowley. After Walker's parents, both Rangers, died in the war, she raised him, along with Lily.
After being carried to General Cross, he thanked him for her incompetence and having left him for dead, stabbed her in the chest, killing her.
As her body wasn't seen later in Vineland's ruins, it must have been taken by the Authority troops to experiment with it. Though she lives on through a hologram. Through it, she leads Walker to get inside Vineland Ark, upon getting the Dash ability and informs him about ''Project Dagger'', the Rangers secret plan to destroy the Authority. Her hologram doesn't appear again throughout the campaign.