Stalker

The Stalker is a zombie introduced in. It is faster and stronger than a Shambler, but not a special zombie or boss by any means. Like other regular zombies, it has four versions, Normal, Fetid, Evolved, and Apex, with each higher evolution gaining more and more buffs (as do all the other normal zombies in the game). The Apex Stalker in particular has a relatively large pool of health for the level it appears in, and can be very dangerous with many combinations.

Trivia

 * It looks more muscular for every evolution, as "the virus has caused extra muscle tissue growth". Also, it loses skin for every evolution like a Shambler.
 * Horns appear on the stalker on every version except the normal version.
 * A little of it's spine can be seen for every evolution, just like the Shambler, but the rib cage cannot be seen for the apex version when it is killed.