Rogue Vortigaunt

The Rogue Vortigaunt is a servant of the Clandestine Company and Captain Vance and appears as a minor villain in Half-Life 2: Episode Four and Half-Life: White Forest.

Half-Life 2: Episode Four (2006)
During the Uprising, the Rogue Vortigaunt captured Alyx Vance due to all the chaos while acting as an ally to her to lure her away into an alleyway away from the sight of rebels. After capturing her, he transported Alyx to an underground cave laying her on a stone, and assured her she will be sacrificed for the vortigaunts.

Half-Life: White Forest (2013)
Gordon Freeman arrives at an underground cave to find the Rogue Vortigaunt preparing a ritual on Alyx along with Captain Vance (Alyx's Uncle) and prepares to kill her. Gordon shoots Captain Vance and holds the rogue Vortigaunt at gunpoint trying to extract information out of him. With little to no info, Gordon finishes off the rogue Vortigaunt with a bullet to the head.

Trivia

 * Like the Half-Life Vortigaunts, the rogue Vortigaunt wears green wrist bands and a collar around his neck, showing that he is a slave.