D0g: The Robotic Protector

D0g is Alyx's massive, loyal robotic companion, built by Eli Vance. He's incredibly strong and agile, capable of throwing heavy objects and smashing through obstacles. D0g acts as a protector and a means of traversal in certain sections, particularly at Black Mesa East. He's not a direct combat companion for most of the game, but his brief appearances are impactful. He's invincible and can clear paths that would otherwise be impassable. His playful nature, especially when interacting with Gordon, adds a unique charm to the game.