Zek is a term that roughly translates to prisoner in Russian. "Infected" Zeks are the result of a Soul Leecher combining with the humans living on Katorga-12. Once infected, they are overcome with a rage and they attack any non-infected beings nearby. They are cunning and will work together to attack threats. Infected Zeks are nothing but a host for some strange and frightful intelligence. They are strong and very dangerous. They have the ability to become invisible and access other periods of time to become out of phase with reality, when Phasing they become invincible and can reach into other time periods to grab weapons. It is advised to use Impulse to pull a Phasing Zek into our time and the Volk S4 Shotgun is advised when fighting them.
Zeks wear a prison jumpsuit that is torn apart or a uniform similar to that of a Spetsnaz Soldier, as seen written in Cyrillic on the back of the creature's vest. (depending on which you fight). They have a muscular body and pale blue skin. Upon seeing their faces, one can see that their eyes glow light blue and they don't have lips. When they phase, their eyes and mouths will glow white. Some zeks have glowing chests that glow greenish in colour that reveals their rib cage under their pale skin. They also possess a tumor growing from their back (possibly from the mutation) Some also look like their head is partially split (likely a result of the extreme properties of E99).
- The Echo Zek is a special kind of Zek , which you will only meet twice in game. They are thinner than a Zek and have a sharpened, bloody plank of wood, complete with nails, attached to its arm. Only two of the abominations are encountered throughout the course of the game.
- There is also a "Zek king", it is incredibly tough and strong. It possess a crown and body armor made from metals that it has found. Only one is seen in the game, and is eventually fought and killed by Renko.
- Another type is a large creature known as a Fatty Zek. A massive creature with mangled military vest stretched over it's chest. It has what is speculated to be the tail ends of Soul Leeches sticking out of the back, and grotesquely deformed. It only will attack the player if it gets too close, with a swat of its arm. If any Dead Zeks are in the vicinity, it will force a Soul Leech out of it's arm towards it's fallen comerade. Ressurecting it when the Leech makes contact.
- A special Red Zek was available for multiplayer mode for those who pre-ordered the game. (It is only a skin)
- Soul leechers are ghost like creatures that turn humans into zeks(it is unknown if this just works on humans).In the zek king boss one flys out of the enemy from its weak spots after Renko shoots them.It doesn't directly attack Renko.
In multiplayer, Zeks can use a variety of moves including:
- Melee- Punches and kicks. If used in mid-air, then the Zek will do a body-slam on the ground. The higher you are, the more powerful the attack.
- Phase- Goes into Phase and becomes invincible but can still be pulled out with an Impulse. It slowly uses Creature Energy
- Barrel- Pulls an Explosive Barrel out of nowhere and you can throw it. These can still be caught and thrown back like in the Campaign.