Zombies are creatures that have reanimated from the dead. They appear prominently as a running gag during the course of the Saints Row games and zombie homies can be unlocked in Saints Row, Saints Row 2 and Saints Row: The Third.
Normal Zombies appear in every level, usually their faces look skeletal and they have blood stains all over their clothes, or they look disfigured and really gory. Tall Zombies appear in Wave 2 and every wave after that, they are several feet taller than other zombies, although they seem headless, their heads aren't completely severed and are hanging down their back, they are tougher than normal zombies but can't bite. Flaming Zombie appear on wave 3 and the last wave after that, they are permanently on fire and can set fire to anyone they touch, and they do not take damage from fire. Exploding Zombies appear on wave 4, the finale wave. These zombies are small and coal black, they are also very weak, but explode when they die or touch Playa.
Zombies appear on Arapice Island after "Air Steelport", as a result of several strange gas canisters rupturing from the falling cargo of STAG's plane. They attack anything on sight. Zombies are very weak and usually die with only a bullet or a punch.
A zombie brute appears in "Zombie Attack", but does not spawn normally outside of the mission. Zombies brutes are much weaker, and take more damage when they are on fire.
If the Zombie virus is given to Oleg at the end of "Zombie Attack", a Zombie Horde is unlocked as a set of Homies; when called, they arrive in groups of four in a DonoVan.
Zombies act like a "Gang" during Zombie Survival, and send zombies in damaged Reapers and Ambulances. At level three notoriety, they send zombie STAG members and zombie Brutes, although they are not marked as Specialists on the map.