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"There you are! I wondered what was keeping you. Hope you didn't have any trouble finding me."
Alyx Vance[src]

The Hydra[1][2][3][4] is an enemy cut from Half-Life 2 during the later stages of the game's development.[3]


E3 Hydra tunnels

The Hydra impaling an Overwatch Soldier in the E3 map "e3_hydra".

The Hydra, a worm-like creature, was to be a massive colonial organism made out of three neon blue tentacles that went up to the surface. Each tentacle was to end with a different "head". Its body was to be made of gelatinous, transparent flesh, with organs clearly visible. It was to be seen in the underground sections of City 17, and along outside canals.[2][3]

Its earliest use was consisting of a scripted sequence set in the City 17 sewers, during which an Overwatch Soldier is impaled by one of the three heads, right after Gordon catches up with Alyx, her telling him "There you are! I wondered what was keeping you. Hope you didn't have any trouble finding me." when noticing him, then saying "uh-oh" when the soldier and the Hydra appear. It was showcased at E3 2003 as a demonstration, in the map "e3_hydra", as well as the first Half-Life 2 trailer. The same area can also be found in other E3 maps, such as "e3_strider" and "e3_sewer".

More recent maps present in the playable Half-Life 2 Beta suggest it was to be met as a boss at the end of the underground levels of City 17, during the Uprising. These areas are now partially included in the Half-Life 2 chapter Anticitizen One, while others, designed specifically for the creature by Ken Birdwell,[2] such as "d3_under_01", "d3_under0102" (featuring 10 Hydras, Metrocops being impaled by them and Manhacks) or "d3_c17_08", have been completely removed (a self-explanatory text, "Final Hydra battle will occur here", is present in "d3_c17_08").[3]

The deployment, left and right movements of the Hydra are completely controlled by the game code. The only real model animations are when it is idle and when it strikes, as well as the scripted animations for "e3_hydra".

Behavior and skills[]

Hydra sketch

Concept art for several heads, including the pointed one and the "smacker" one.

One of its "heads" was to be pointed and capable of piercing through its victims, while the other's behavior is unsure. The pointed head model is unnamed and appears first in the scripted sequence; the two others appear right after, at which point the scripted sequence stops. One is named "seer", the other "smacker". "Seer" was probably to act as some kind of sensor (given its name and its finger-like protuberances), while "smacker" was probably to smack victims like a fist, or grab them like a hand, given its shape.


Valve's Ken Birdwell was responsible of the Hydra's coding and AI development. It was his pet feature, and a monster he wanted in Half-Life 2 from the start. Designing whole areas of the game around it, he personally spent about six months on and off getting all the movement algorithms and physics to a working state. Everyone at Valve was pretty skeptical about his work on the Hydra when he started, so he kept it pretty low profile. However, once he got some of the early rough Al drafts up and running and showcased it to his colleagues, they got very excited about it and started pushing him to hurry up and finish it.

But the closer it got to being done, the more its fatal flaw was becoming clear: while this great big glowing giant worm looked quite awesome while fighting other NPCs, snaking through the map, knocking stuff over and putting on a great show, it was unsatisfying in the first person, looking no more than a non-descript blob doing something vague, then the player would be dead without being able to see properly what they were fighting.

It then had to be cut. It was personally very painful for Birdwell, but he states it had to be done since when a design is not working, it has to be given up. However he adds he would still like to see the Hydra in the Half-Life universe somewhere, suggesting he would start by rethinking its Al more along the lines of an Antlion.[2] This however has not been made yet, although the npc named "Surface" used in the Source Particle Benchmark uses a model named "Hydra.mdl", but it is different. The Particle Benchmark files also feature Hydra textures.


  • In the scripted sequence, the Overwatch Soldier utters a normal human scream, without vocoder effects.
  • The Hydra's pointed head looks similar to the Tentacle enemy from the original Half-Life.
  • The Hydra is not affiliated with any faction and is independent. It will kill anything, Combine, Rebel, or otherwise.
  • The Playable Beta also features another Hydra model, hydra.mdl, which does not have visible organs.
  • This enemy likley inspired the hydra from the 2 prototype games.



Hydra about to impale a Combine Soldier.

List of appearances[]


External links[]