The deathclaws were originally created before the Great War by the government to replace humans during close-combat search-and-destroy missions. They were derived from mixed animal stock and then refined by the Master, using genetic manipulation. The resulting creature is almost unbelievably fast and powerful.
Around 2161, deathclaws were still mysterious and legendary creatures to many inhabitants of southern California. They could only be found in the Boneyard at the Warehouse, with a mother living there, one in a former deathclaw's nest and around the Hub, sometimes attacking caravans or travelers. Later, as the deathclaw population grew and really spread across the continent, the deathclaws stopped being perceived as legendary beasts, and started to be seen just as another dangerous creature.
Deathclaws have a hunchbacked, bipedal reptilian build with long humanoid arms. They stand roughly nine to ten feet tall, with a thick and resilient hide, powerful muscles, and twelve-inch-long, razor-sharp claws that can kill almost any other creature in only a few swipes; hence their name. They have an excellent sense of smell and hearing, though their eyesight is poor. Their build gives them incredible speed, agility and strength in close combat, making them an extreme threat. Though they were originally mutated chameleons, they have lost the ability to camouflage themselves.
Deathclaws are very aggressive, territorial, and carnivorous. They typically live in small packs of around eight to twenty members led by an alpha male, who is the only one allowed to mate with the females. Deathclaws are oviparous, with the eggs typically laid in dark, sheltered locations and fiercely guarded by their mother. Young deathclaws reach maturity under the care of their parents, following them closely until they are old enough to fend for themselves.
Although they do not have vocal cords, they can growl and shout, and some seem to be able to mimic human speech much the same as a parrot does. However, normal deathclaws aren't intelligent enough to be capable of real speech.
Interestingly, deathclaws do not sharpen their claws on nearby objects, instead preferring their own nails to do the sharpening. The Lone Wanderer or Courier can witness this behavior while sneaking up on a deathclaw.
Deathclaws really live up to their name in Fallout: New Vegas. The game introduces several new variations of the creature, and they are found in much larger numbers. However, unlike in Fallout 3, deathclaws are never encountered randomly, and always appear in specific locations. Most deathclaw variants are armored, making them more resilient against attacks. Their Damage Threshold is 15, equal to that of a suit of combat armor. The amount of damage they do to the player ignores their DT.
There is also a deathclaw-filled cave called Dead Wind Cavern. Here you can find a mother deathclaw with some deathclaw babies, along with average deathclaws and the unique legendary deathclaw, the most powerful creature in the Mojave Wasteland. There is a unique grenade machinegun named Mercy in the room with the legendary deathclaw, on a dead Brotherhood of Steel Paladin. Another location to find deathclaws is the Gypsum train yard, where the vast majority of the deathclaws are blind. Depending on your level they will either be regular, young, or blind.
The deathclaw alpha male is similar to a legendary deathclaw in appearance, but with darker skin. Although not as fierce as the legendary deathclaw, they are still twice as strong as a regular deathclaw and run much faster. They often travel in packs with other deathclaws. One can be found at Quarry Junction, and several cluster together in the deathclaw promontory.
Matriarchs of the deathclaw broods, deathclaw mothers are bigger, stronger, and more aggressive than the standard deathclaw. They are second only to the legendary deathclaw in ferocious might. They are commonly mated with the deathclaw alpha male. They are very thick-set and heavily built deathclaws with dark blue colored skin, giving them an intimidating look. Deathclaw mothers are notably the only breed of deathclaw with spiked tails and horns that sweep backwards. They usually reside in dark areas near their young or their eggs, and they are more than eager to tear apart anything that the Wasteland throws at their babies. They are even faster than a deathclaw alpha male. Deathclaw mothers do not respawn.
Deathclaw babies are the youngest and smallest of the deathclaw species. They can be found throughout the Mojave Wasteland. While they are no real threat by themselves, they are always found following a deathclaw mother. If one of them is killed in the mother's presence, she'll be driven into a frenzy.
These immature deathclaws are about the size of a human. Their horns are not fully grown and their skin is much lighter than grown deathclaws. This makes them easy to pick out among regular deathclaws. Although normally easy to kill for higher level players, they tend to cluster near the adults.
Contrary to the name, blind deathclaws actually have a higher Perception than regular deathclaws, making them harder to avoid thanks to their heightened senses. However, their attacks are weaker. Even though they cannot see, their alertness to your presence will in fact alert all other deathclaws nearby of your position despite the one that found you being blind.
One of the most dangerous creatures in the Mojave Wasteland, the legendary deathclaw is found in Dead Wind Cavern and has distinctively long horns, a light olive coloration, and striped tails. It is also one of the largest enemies in the game (along with the X-42 giant robo-scorpion and the giant ant queen), towering over other deathclaws (themselves roughly 10 feet) with its massive 15–17 foot stature. The legendary deathclaw also deals enormous damage (twice as much as ordinary deathclaws) and can bring down even the hardiest player character in only two or three hits, all while having the third largest amount of Hit Points in the game, behind the X-42 giant robo-scorpion and the legendary bloatfly. Despite its size, the legendary deathclaw can move faster than its normal counterparts, and has been known to make successful leaping attacks from a huge distance.
Deathclaws found in The Divide level with the player, increasing in power at player levels 30, 40, and 50. At higher levels they are noticeably more powerful than deathclaws from the Mojave Wasteland, with higher health and a much more damaging melee attack, surpassing even the legendary deathclaw in damage when at maximum level (though doesn't surpass it in health, being only 700hp compared to the 1,000).
These variants are introduced by the add-on Lonesome Road, and can only be found along the The Courier's Mile and among the ruins of Hopeville. Their statistics are varied according to the player's level, making them very dangerous if the player is near the level cap. Appropriately so, Irradiated deathclaws also deal radiation damage. Unlike other variants, irradiated deathclaws have zero Damage Resistance/Threshold.
The recent patch has made all deathclaws in the Mojave Wasteland (except those in The Thorn) as tough as the ones in Quarry Junction. As a result, non-Quarry Junction deathclaws have 500 Hit Points, compared to just 250 hit points prior to the patch. Some of the other deathclaw variants have also had their health increased (i.e. young deathclaws now have 350 Hit Points, and the legendary deathclaw's Hit Points has been increased to 1000 compared to 850 prior to the patch).
The flare gun causes abominations such as deathclaws to flee.
Following the recent patch, it seems deathclaws will stop respawning in certain areas. These areas include Gypsum train yard, the outskirts of Quarry Junction, as well as other locations.
Crippling their legs will both reduce deathclaws' speed to a limp and make them unable to perform their jumping attack.
Young deathclaws and baby deathclaws will run away from the Courier when severely outmatched.
Deathclaws will give up searching for the Courier when he or she is in water.
Deathclaws are able to detect you while sneaking with a Stealth Boy activated from farther away due to their high Perception.
While deathclaws are no longer randomly encountered like in Fallout 3, they have a tendency to gather in "colonies" of ten or more. If you see one, there are likely more around.
Young deathclaws still drop deathclaw hands, even though their actual hands are significantly smaller than it.
In the Lonesome Road add-on, there is a unique deathclaw called Rawr, found in a cave in the Divide canyon. Its attacks are far more damaging than its legendary counterpart, and it is much faster as well. When killed, it drops the item Rawr's talon, which can be crafted at workbenches into a unique deathclaw gauntlet called the Fist of Rawr (or Fist of the North Rawr with Wild Wasteland).
Oddly, a deathclaw egg can sometimes be looted off the body of a deathclaw alpha male. This is an oversight.
The deathclaws will stop searching for the Courier if they stand on a rock high enough that they can't reach him/her.
Sometimes deathclaws will follow the Courier inside shacks, making it even harder to kill them.