Stalker

"This is what happens to you if you resist.. or if you're just in the wrong place at the wrong time."

- Alyx Vance

The product of extreme, brutal Combine engineering, a Stalker is a human who has been experimented on by Combine scientists, has their personality totally erased and replaced with Combine servo-programming, nano-devices embedded into their skin, and their bodies physically altered. Their limbs have been removed and replaced with mechanical extensions; most organs, excess fat, as well as muscle have also been removed and what appear to be metallic augmentations added to parts of their body. "Stalkers", the codename by which the Combine know them, appear to be in constant pain, as their loud wheezing indicates. A stalker can't talk, and instead can only make roars, most likely because its vocal cords, or perhaps entire larynx, has been removed, as the metallic hole in their throats suggests. For ease of maintenance and to bring a physical dependence on the Combine, the stalker's digestive tract has been removed, resulting in the stalkers surviving solely on a saline solution that the Combine provides. Stalkers would originally have to work to gain the metallic legs, proving they could be trusted with additional movement. All stalkers appear to come from men, as they have a male facial shape. However, this may simply be a developer oversight. It could also be that their bodies are so radically altered that the entire concept of gender no longer applies to them.

These people are turned into stalkers at Nova Prospekt, and are then transported to the Citadel to do slave labour for the Combine. They are transported by Razor Trains, and are confined in pods during the transportation. Despite being seen in Nova Prospekt and the Citadel, stalkers are never actually engaged in combat during Half-Life 2. However, it is possible to engage in combat with them in order to more easily achieve mission objectives in Half-Life 2: Episode One, as their lasers prevent certain tasks from being completed. Episode One is also where the exact nature of stalkers is first revealed. In Episode One, the player and Alyx enter the Citadel. After a bit of progress, the player and Alyx enter a room with two stalkers working a forcefield, temporarily preventing progress. Alyx states that the stalkers "shouldn't bother us if we leave them alone". Interestingly enough, when the player is in the core of the Citadel and chooses to kill one of the two stalkers, the remaining one will turn to face the player and roar at Freeman. The stalker will then proceed to attack the player with the laser tool. Contrarily, if the player is fast enough to cross a field bridge there before it deactivates, Stalkers can be approached face to face, and do not attack the player but instead walk away as if he wasn't there at all.

It appears that the citizens of City 17 have a full knowledge and understanding about stalkers, what they are, and how and where they are "made." Alyx Vance comments on Nova Prospekt: "It used to be a high-security prison, it's something... much worse than that now." Barney Calhoun also makes the comment, "He was about to board the express to Nova Prospekt!" at the start of the game. However, this knowledge may just be limited to members of the Resistance



Behind the scenes
The Stalker was originally planned to be fought in Half-Life 2, but this feature was cut and, later, re-introduced in Episode One.

Trivia

 * Stalkers can be spawned via the console in Half-Life 2 itself, but it will crash the game if they are killed, a result of not having a death animation. This can be fixed by installing Garry's Mod. In Episode One, spawning works normally.
 * There is one stalker related achievement, Pacifist. Do not kill either Stalker in the core room to get it.
 * The Stalkers in the Half-Life 2 Beta had melee attacks, their laser attack did more damage and they would emit a high pitched scream when killed.
 * SMOD has a full working Stalker NPC that attacks the player and other non-Combine NPCs. It also has its own ragdoll.
 * Stalkers are not encountered in Half-Life 2: Episode Two but they can be spawned in the Console Menu.
 * Stalkers are zombies in GMOD's game mode, Zombie Survival, under the name "Wraith".