Deathclaws are a fictional race race of evolved reptilians in the Fallout universe. Mutated from a horned variety Jackson's chameleons, Deathclaws are large (3-meter tall), highly aggressive bipedal carnivores. They are very strong, fast, and tough, making them a challenge for poorly equipped characters.
In Fallout 1, Deathclaws are viewed with almost superstitious dread by those who know of them. They are thought to be "ghosts of the war", vicious and nearly indestructible.
In Fallout 2, it is revealed that the Enclave attempted to convert Deathclaws into soldiers; using a modified F.E.V. to increase their intelligence. The experiment succeeded too well: the Deathclaws realized that they were enslaved, and feigned unintelligence until they could escape. These intelligent Deathclaws, capable of speech and reason, created a peaceful community within the abandoned Vault 13. The Chosen One (the player) can interact peacefully with these Deathclaws, who do not harm humans, even permitting humans to leave freely among them. If the Chosen One chooses to aid the Deathclaws, one of them, a scholar named Goris, will be available to join the party. Goris cannot wear armor or use weapons other than his own claws, but is quick, tough, and can do heavy damage with critical hits.
The average intelligence of a modified Deathclaw is that of an eight-year-old human. However, they vary widely in this regard, with several individuals approaching or exceeding average adult human intelligence. When encountered in Fallout 2, they are using selective breeding in the hopes of producing stronger, more intelligent offspring.
In Fallout: Tactics, a Deathclaw Matriach is enslaved by the Beastlords. If she is freed, the character can recruit intelligent Deathclaws into his or her party. All Deathclaws in Fallout: Tactics appear to be intelligent, though this game may not be canonical.
Wild Deathclaws in all three games will attack the player on sight. Deathclaws allied with the player do not seem to mind killing their feral brethren.