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, primarily build off of the very popular Jackson Chameleon. They were then refined by the Master, using genetic manipulation and the FEV virus. 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.
The variants that can be encountered are based on level. Different variations become increasingly more common with higher levels. For example, where one might expect to encounter a normal deathclaw, they might encounter an alpha deathclaw once they pass a certain level. The higher the player's level, the more chance of the next difficulty of deathclaw to spawn in its place. Scripted encounters, such as on top of Haymarket Mall and at Lynn Woods, have a higher chance of spawning a next-stage deathclaw than randomly encountered wasteland ones.
Normal deathclaws, defaulted to level 22, are highly dangerous for those poorly leveled and still present a challenge at higher levels. Deathclaws will charge the target while defending their weak belly with their head making it difficult to land a shot to the weak spot even in V.A.T.S.
An alpha deathclaw can be encountered by flipping the breaker at the top of the tower in Lynn Woods and the roof of Haymarket Mall (two may spawn on the roof). They may also be encountered in the Glowing Sea and west of Natick Banks. Alpha Deathclaws have horns that spread foward and up, while a regular Deathclaw is forward and down. Alpha Deathclaws also have rust-coloured skin.
The glowing deathclaw is a highly irradiated version of a deathclaw. A green light emits from the skin between their scales, and they inflict radiation damage on top of their massive ballistic damage. They can start spawning in as low as level 25, replacing several randomly-encountered deathclaws including those above Haymarket Mall and Robotics Pioneer Park.
Matriarchs have less health than an alpha, but more than a normal deathclaw. Their horns curve out and down, compared to the alpha's forward and up.
They start to appear when the player is around level 35, and will replace some randomly encountered deathclaws in the wasteland.
A scripted Savage Deathclaw may be found in the Museum of Witchcraft. This event is leveled and part of a side mission. The Sole Survivor can choose to fight but can also run away or sneak through it. If the player has a high enough level, they may encounter Savage Deathclaws in random encounters, such as within the Glowing Sea or near Natick Banks. A Savage Deathclaw is probably a Deathclaw Matriarch with a broken horn. This can be proven by both of them having the same colour skin, the yellow lines on their body and the spread out horn.
The albino deathclaw is a pale version of the deathclaw, with more health, that can be encountered after reaching level 71. This deathclaw type's high health can make it a worthy adversary and it will only lose 1/4 of its health from a shot from the mysterious stranger.
The chameleon deathclaw will begin to spawn at Level 81. Its default color is a slightly more sandy tone of a regular deathclaw, but when aggravated, it will display vibrant colors depending on its movements in battle. It flickers between gray and acid green, red, and orange and teal. When killed, its body retains the last color it was displaying.
Mythic deathclaws are the highest non-legendary tier of all deathclaw variants and can be encountered starting from level 91, although on rare occasions they can be encountered from level 75 onwards. These deathclaws level with the player, so the skull display on their name never goes away and renders them immune to the Wasteland Whisperer perk.
All over the Commonwealth as random encounters, including possible attacks on any owned settlement.
On the Garden Terrace on the roof of Haymarket Mall.
Two random encounters can be triggered by throwing the switch on top of the tower in Lynn Woods.
One can be found guarding the entrance to Old Gullet sinkhole.
A scripted deathclaw can be encountered in the Museum of Witchcraft.
A level-dependent deathclaw can be encountered just south of Capsized factory on the top of a hill.
A scripted deathclaw can be found in a tunnel off the gym area in the Boston mayoral shelter.
A scripted deathclaw can be encountered in Kendall Hospital.
A group of deathclaws fighting a behemoth can be found west of Natick Banks, along with several more in and around the area.
One can be found in the Robotics Pioneer Park, inside the first house from the fast travel point.
A level-dependent deathclaw variant always spawns outside of the rocky cave, usually asleep in a small bedded area.
A leveled deathclaw will spawn in the lower parts of the parking garage.
In the quest The Devil's Due when returning the egg, the deathclaw guarding the nest is scripted to be permanently friendly to the player and their followers as long as the nest is not interacted with after the egg is returned.
It is possible to shoot/dismember the tail off of a Deathclaw and for it to still live. Likewise, it is possible for an Alpha deathclaw to spawn by the Lynn Woods siren that has no tail.
Trying to dismember a dead deathclaw can cause the game to freeze.
↑Deathclaws being genetically engineered before the Great War and later refined by the Master is mentioned in the Fallout 2 Official Strategies & Secrets strategy guide, written by Fallout 2 lead designer, Matt Norton, as well as in Fallout Tactics. It is unknown why the Master would genetically manipulate the deathclaws and then not use them at all for his purposes.