The Defiler is a Zerg Hive tech unit. It is one of the Zerg's most powerful spell casters. A support unit, it is most well known for its Dark Swarm and Plague abilities.

The Defiler is late game unit requiring the Hive and Defiler Mound, at which time it can be morphed at any of the Zerg player's Hatcheries, Lair, or Hive. It does not deal any damage directly, thus is easily susceptible to opponent attack. As such, Defilers usually travel along with Zerg armies as a support unit rather than traveling individually. Despite this, Defilers are relatively slow and move in an inelegant slither, and thus easily fall to the rear of the Zerg forces. To mitigate this, it is common for the Zerg to transport Defilers in Overlords and as part of a drop attack. Defilers are most commonly used against Terran and Protoss, against whom their spells are most effective.