The Ganados (or Los Ganados) are the infected villagers of the sleepy, rural community of Pueblo in Resident Evil 4. They are essentially brainwashed slaves, driven by the Las Plagas parasites, doing the bidding of the Las Plagas leader (Osmund Saddler).
Though not zombies, they act and attack whoever they deem as enemies in a similar, shambling manner. The Las Plagas parasites have given them all increased endurance to pain and bodily damage, making them a considerable threat. Occasionally, when a Ganado has lost its head, an evolved Las Plagas parasite will emerge thereout and attack Leon. An exposed Las Plagas can be killed by a bright light, such as one from a flash grenade.
The first Ganados that Leon encounters are the regular villagers, usually middle-aged men and women of the community, who were clearly farmers and fishermen in their previous uninfected lives. They attack mostly with rural tools such as pitchforks, torches and sickles. Some have dynamite, as the town was involved with mining at one point (as this was how the Las Plagas was uncovered).
A particularly difficult variation of the normal villager is "Dr Salvador": a chainsaw-wielding, burlap sack wearing villager who is able to kill Leon in a single attack, should he get close. The game recommends evading him whenever the enemy appears; though with enough firepower he can be killed for a valuable item. The Bella Sisters are similar Ganados, with face-obscuring bandages and chainsaws of their own.
The Zealots, who reside in Ramon Salazar's castle, are a stronger variation of los Ganados. The Zealots speak in Latin, and are considerably more dangerous. Several are armed with medieval weapons, such as morning stars and crossbows. Some have additional protective gear like large wooden shields, to block attacks, or iron masks to prevent headshots. The Zealots, in turn, are less active than the villagers, being more zombie-like and inattentive.
Saddler also has his elite Las Plagas militia: Ganados with their own weaponry which are situated in vital areas. A special version of these militia Ganados, named J.J., is armed with a powerful mini-gun.
Finally, there is the Merchant. Though clearly a Ganado, per his eyes and pale complexion, he appears to still have his own free will and will assist Leon by trading items with him. Like the other "special" Ganados, his body doesn't disintegrate, and he will later reappear if killed.