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Synths are a collection of various species that are cloned cyborg and biomechanical aliens used by the Combine as war machines for their army. Being an invaluable resource for the Combine, they are highly resilient to damage and are used for invasions and suppressing uprising.


D3 citadel 050339

Crab Synths and Mortar Synths being transported on a conveyor belt.

Synths are officially described as "self-replicating robots that evolve", "created or taken over by the Combine and enslaved during their conquests and wars."[1] All Synths seem to possess both organic and robotic characteristics, suggesting that they're the synthetic derivatives of alien species that were previously found by the Combine, and modified to their needs.[2] They vary in shape and size depending on their function, but are recognizable by what appears to be a fusion of mechanical and organic parts. The name 'Synth' itself is derived from 'synthetic' in reference to their nature as synthetic organisms. Synths commonly appear to have organic structures such as compound eyes, segmented legs, and an organic looking skin which, with some exceptions, mostly have a sand-brown color. These features are heavily contrasted by the mechanical components installed in their bodies such as weapons, propellers, or propulsion engines.

Due to their alien nature, Synths have remained largely a mystery. It is unknown whether these creatures were originally part of a native species that were enslaved by the Combine or artificially evolved. If the former is the case, it is also unclear whether these creatures originally resembled their modified selves as the line between their organic and mechanical components are seemingly different for each Synth. For instance, Striders are shown to have a brain along with what appears to be a spinal cord and a muscular system in Episode Two indicating pre-existing organic components while the Shield-Scanners appear to be mostly mechanical and seemingly reliant on batteries like a machine. Synths, however, do seem to require maintenance presumably due to their mechanical parts, as Stalkers can be seen working on Gunships in the lower levels of the Citadel. Synths are also never observed to be "self-replicating" in-game or capable of reproducing by themselves, but rather seem to be artificially raised or manufactured by the Combine. Whether they are produced locally on Earth or brought in from an external location is unknown.

Synths are for the most part highly resilient to damage. Their carapace-like armor is largely immune to small arms fire with bullets unable to penetrate the tough outer shell. Two notable exceptions are the Hunter, who is nonetheless highly resilient to bullet damage, and the Shield Scanner, who can be easily taken down with just a pistol despite seemingly sharing the bulletproof sand-brown carapace as larger synths. These tough outer shells are mostly impenetrable by conventional means, though they can be ripped open with enough force as demonstrated when Dog tears a piece of a Strider's carapace off in Episode Two, . The only weapons that are known to be effective against larger Synths are explosives such as the RPG or the MP7's secondary fire, the Combine Energy Ball, and the Magnusson Device. With the exception of the latter, it takes a significant amount of each of these resources to take down one Synth, let alone several. This durability make combat Synths an invaluable resource for the Combine in the battlefield, where their presence can quickly turn a battlefield on their favor.

Synths appear to be a staple of the Combine's army outside of Earth as well. Gunships were seen coming from a location assumed to be the Combine Overworld or another Combine-occupied world during Wallace Breen's attempted escape at the Citadel's Dark Fusion Reactor, showing that they are part of the Combine's forces elsewhere. A Strider can be seen in a newspaper photo as part of an article detailing Earth's surrender, indicating they were in use during the Combine's initial invasion of Earth. Since the human-derived forces of the Combine and repurposed human technology such as APCs or Hunter-Choppers only appeared after the Combine established themselves on Earth, Synths were likely part of the Combine's invasion force on Earth. This could potentially mean there were types of Synths used during the invasion that are currently not on Earth as well as others yet to be encountered by the human species.

Known Synths[]

Dog vs Strider Outlands

Dog attacking a Strider in the Outlands, as seen in the second Episode Two teaser trailer.

Various types of Synths have been brought over to Earth by the Combine after their victory over Earth's forces. Some, such as the Shield Scanner, are merely used as scouting or transport and have little to no weaponry. Others, such as the Strider and Gunship, are infamous among the remaining human Resistance as fierce war machines. However, some Synths have remained unknown since they have not been encountered yet or are only deployed on certain situations. Currently, the Synths that have been shown on Earth are:

Behind the scenes[]

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Combine Gunship factory in the Citadel.

  • According to Dhabih Eng, the team tried to incorporate elements that were neither strictly organic nor purely mechanical to suggest their original organic forms. They did not want to have giant alien creatures with armor attached or implants added, but rather show a forceful evolution of the equipment unnaturally imposed on them by the Combine. In the end, the designs intentionally blurred the line between machine and animal, in their appearance and more importantly their motion and how they reacted to the world around them.[1]
  • According to the book Raising the Bar, the idea was to start Synths as androids or synthetic creatures that have been enslaved by the Combine through conquests and wars. Mentioned as "Self replicating robots that evolve", instead of having to be maintaneed, repaired or upgraded, they would make a new version of themselves every five years. Ted Backman says Synths were inspired by the android Bishop, featured in Aliens.

Cut Synths[]

Several Synths were cut from the final game:

Early Synths[]

Several pre-release materials gives some insight about the early Synths.

"Weather Control Vignette"[]

Raising the Bar features a story fragment of the Weather Control chapter given to the developers for design inspiration, relating parts of the Weather Control battle, with early names for the Combine units. For example "mech" seems to stand for the predecessors of the Synth, while "mech carrier" likely refers to the Combine Dropship. The text depicts the mech looking like Dog's cousins, but apparently new-minted and flawless, and with a "head" in quotes, suggesting that it is strangely-looking. Also, at some point in the text, its head pulses with a faint glow as if powering up for energy, then fires, which is very similar to the Strider's warp cannon, added to the fact that it is brought by a "carrier", the Strider being brought by Combine Dropships without their containers. Added to the gun located in its head, it also has mounted guns.[1] This "mech" could be an early version of one the Synth predecessors of the Overwatch Elite, the Combine Synth Elite Soldier, which has been through several iterations with strangely-looking heads and a narrow waist like Dog (as in the picture seen here), or the Combine Super Soldier, also with a strangely-looking head.


A folder called "TBot1" can be found in the model textures files from the playable Half-Life 2 Beta files, in a folder called "obsolete". These are likely the textures for the early "mech" or (ro)bot from the Weather Control story fragment, a very early NPC, since they possess some similarities with Dog in design, mirroring the Weather Control story fragment covered above. Since Dog is said to be one of the few concepts that went from the first sketch straight into the game with relatively few changes to the design,[1] it could be assumed that the Weather Control mechs are two-legged and bear similar colors and body part plates to Dog, since he was made from scraps from different metal sources, such as Combine metal (an old texture file for Dog also shows a "15" like logo also found in the TBot textures).

The textures also suggest a slightly battered robot and show round eyes that recall the City Scanner's eye (Dog's head). They also show that a yellow color scheme was to be used, and suggest that a bipedal, paw-footed design like Dog's was also to be used. The model is however missing, and it is next to impossible to guess its shape from its texture files. The "1" in the folder's name also suggests that there were probably other versions, (such as non-battered conditions or other colors). Other texture files suggest that TBot had an antenna and was equipped with a flamethrower, and that some of its internal circuits were to be visible and blue, like the early Combine Dropship, the Crab Synth and the Mortar Synth. The files also suggest a "collar" made of green fabric, with the same fabric on one shoulder and the thighs, showing another example of the old concept of the Combine recycling human materials.

The TBot ("bot" implying "robot") seems more mechanical than other Synths found throughout the universe. It appears to sport several cogwheels and pistons on its body, more in line with the "Combine recycling human materials" mood of the very early Half-Life 2 storyline. Overall, the TBot design appears to be much closer to the "mech" from the cut Weather Control story fragment, making it a likely an ancestor of larger, two-legged Synths like the Combine Synth Elite Soldier or the Combine Super Soldier.



A variant of the TBot1, with green eyes, the colour of the robot is unknown, because the TBot in concept art is obscured.

All existing TBot 2 files were deleted from the retail version of HL2.

"Alyx Vignette"[]

A story fragment from Raising the Bar is set at the start of the Air Exchange chapter and has Gordon involved in a train wreck. Alyx, accompanied by her pet Skitch, encounter Gordon before being attacked by "tripods" (i.e. Striders) and "Combine Elite": tall, metallic shapes making muffled, almost silent movements. The description does fit that of the Combine Super Soldier (named "Combine Elite" in Raising the Bar[1]) while also vaguely matching the Combine Synth Elite Soldier, another elite Combine unit. Also stated in the book, the Elite was turned into the humanoid unit seen in the final version.


Gunship logo

The Gunship back logo.

Most Synths bear at least one logo. Gunships and Striders bear the same logo on their back and head, respectively. This logo was on the back of the Overwatch Soldier's old texture (in white) and can also be seen on the shoulder of one of the Combine Synth Elite Soldier versions. Its meaning and relation to the Combine are unknown, as are the possibilities of it proving any relations between the Strider and Gunship. Other Synths such as the Shield Scanner, the Dropship and the Advisor Pod bear the standard "claw" logo (in dark red for the first two and white for the latter), while the Shield Scanner also bears a trimmed "CMB" logo (like the City Scanner). The Mortar Synth, Crab Synth, and Hunter bear no logo at all.

Combine soldier beta back logo

Beta Overwatch Soldier version.

As for the cut Synths, the Wasteland Scanner bears the standard "claw" logo (in dark Red), and other unknown markings, partially seen in the Overwatch Soldier outfit. The Combine Guard has no logo, while its predecessor, the Combine Synth Elite Soldier, has some informal logos in some of its versions, as well as the Gunships / Strider logo, as stated above. The Sacktick has two informal logos, one on its back, one on its right front leg, not seen elsewhere. The Combine Super Soldier has the number "314" in its concept art (also featured in the Beta Overwatch Soldier outfit), and two Red triangles in a Red-rounded circle, reused for the Overwatch Soldier outfit, although with different colors. It also has Red strips in several locations.


  • The term "Synth" relates to words such as "synthetic", "synthesis" or "synthetical". A "synthetic" element is "made artificially by chemical synthesis";[3] a "synthesis" is "the combining of separate elements or substances to form a coherent whole";[4] and a "synthetical" element is the combination of "separate elements to form a coherent whole".[5] The term "synth" could therefore be interpreted as a short for "synthetic". In a general science fiction sense, "synth" is often synonymous with words like "android", "robot" or "artificial (human)", namely in IPs like those belonging to Philip K Dick and the Fallout series of video games.
  • It could be argued whether Hunters are Synths or Cyborgs since they are vulnerable to gunfire and seem to have an integrated armor instead of a full metal body, unlike other Synths. A blood-like substance is observed on hit, also suggesting organic matter. This also shows that all Synths are cyborgs rather than robots.
  • It is unknown if Synths are the only species/force used within the Combine or if other kinds of creatures exist within the Union.


Retail Synths[]

Cut Synths[]

List of appearances[]


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