Illagers, short for "ill-willing villagers", are humanoid Mobs that look similar to Villagers, except they are hostile toward players. They are considered outcasts from villages. In addition to this, they will also attack Villagers, and both Golems. There are three types: the Evoker, Vindicator, Illusioner.
Evokers and Vindicators spawn in Woodland mansions, while the Illusioner is unused and can only be summoned by commands.
All illager sounds are slightly different from each other, but sound a lot like Villager noises in a "humming" manner.