Dog is a robot, built by Eli Vance to protect his daughter Alyx when she was a child. Dog's original model was around one meter in height, but as Alyx grew older, she began adding upgrades and new parts to Dog, and he towers around 2.5 meters tall at the time of Half-Life 2. Dog has a Zero Point Energy device, much like the Gravity Gun, built into his right hand so that he can pick up and throw things. Dog's body is constructed largely of scavenged scrap metal, hydraulics and wires. He has what appears to be a scrapped Combine City Scanner for a head, though with only three flaps while normally Scanners have four. He is quadrupedal, walking on his knuckles like a gorilla, but can balance himself on his hind legs if it is needed, such as when he's lifting a heavy object. Dog has incredible strength and is able to lift and move very large and heavy objects, even managing to lift up a section of the massive Combine Smart Barrier that surrounded the Citadel. He is able to pick up vehicles such as cars, vans, and APCs with ease, and can throw them long distances with great force and accuracy. He is also strong enough to physically tear apart large and powerful Synth enemies that would normally require heavy firepower to take down, such as Striders.
