The assaultron robot was constructed by RobCo and sold to the US Military as a front-line wartime combatant. It is fast and deadly at close range and employs a devastating laser at a distance. The dominator variant can also use stealth technology.
The assaultron's body bears some striking resemblance to a female figure, coincidental or not, with prominent hips and chest, the latter appearing to house additional servos for the robot's arms, hinting at their strength in melee combat. They are highly aggressive, fast, and some will attack the Sole Survivor on sight, usually using their claw-like hands in melee. An assaultron's head houses an incredibly powerful laser that requires charging up before being fired. The assaultron's face will become surrounded by red electric energy when it is charging its laser beam attack, after which a great laser burst will be unleashed, doing serious damage to anyone who is caught in it. The dominator variant of the assaultron is also equipped with a stealth field.
An assaultron's laser can be halted or avoided by using Jet and stepping out of the way, killing it, or doing enough damage to its head. If it is allowed to charge its laser all the way, and if not blocked by an object, it will inflict devastating amounts of damage on its hapless target, often killing even high level characters or NPCs in seconds. The fact that assaultrons take reduced damage from headshots only serves to compound their main weapon's threat potential; however, one can cripple the head, thus removing its ability to use its head laser.
Assaultrons' weak points are their legs. However, when these are destroyed, the assaultrons will continue to pursue the target by crawling on the ground. After taking sufficient damage, they will charge a potentially deadly explosion as a last desperate attempt to eliminate the target. Killing them before they can activate it will result in a normal death.
Legendary assaultrons will invariably detonate violently, similar to a mini nuke blast, approximately two seconds after they are destroyed.
On lower levels they can be very difficult to face head-on, due to their fast speed and powerful attacks. A low-level player character may have difficulties killing or crippling the assaultron before it is able to get into melee range or charge its lethal laser attack, especially if the assaultron is backed up by additional enemies. A notable ability they have is being able to sidestep, making them difficult to hit, especially with semi-automatic weapons. While their laser is fully charged they are also capable of grabbing an opponent at close range and firing their laser directly into the victim's head, which is a virtually assured death sentence.
Assaultrons' Perception seems to be significantly higher than other enemies', making them difficult to sneak up on and hack without maxed-out Sneak skills, corresponding armor and/or using a Stealth Boy.
Deadly, especially for the unprepared, the assaultron is among the most fearsome robotic enemies in the game. While their usual unarmed attacks are already a challenge for some, the real danger from these enemies comes from their charged laser weapons. The laser cannon that doubles as its head can usually disintegrate victims on contact. Making matters worse, dodging the weapon can prove difficult, since the size of the laser engulfs anything in front of it. Luckily the charge up for this weapon is long and given away by an impressive light show coming off the assaultron's face. A fast fighter may be able to kill it quickly or even get behind it while its firing animation is going.
The Dominator variant has a powerful attack that consists of stabbing the target's torso with two swords simultaneously and spreading its arms outwards, typically resulting in a one-hit kill against low leveled or low armored players.
These stronger variant of the already formidable assaultron can be counted among the nastiest dangers in the Commonwealth. The blades on its arms give its unarmed attacks considerably more power while its head laser will still be gunning for its target. The Dominator's true danger is its unique stealth capability, making it difficult to target, especially in VATS, before it gets into melee range.
The Gunner assaultron is the same as the basic assaultron, except it has the Gunners symbol painted on its chest, in place of the star and USA markings. They are frequently found at Gunner bases and outposts.
The Gunner assaultron invader is the same as the assaultron invader, except it has the Gunners symbol painted on its chest, in place of the star and USA markings. It is frequently found in Gunners bases and outposts.
The Gunner assaultron dominator is the same as the assaultron dominator, except it has the Gunners symbol painted on its chest, in place of the star and USA markings. One replaces Tessa after she is killed at Quincy ruins.
Assaultron devils are a modified variant of the assaultron created by the Rust Devils. It is weaker than the normal variant. Their hands are replaced with construction claws and they are covered in scrap armor.
Assaultron gorgons are a modified variant of the assaultron and are created by the Rust Devils. Wielding two shishkebabs, they are the most powerful assaultron variants of all and are dangerous opponents.
One can be found with Ivey in Fort Hagen hangar and others can sometimes be seen with Rust Devil patrols.
Novatrons are the base Nuka World variation of an assaultron. They can be found in the Galactic Zone in Nuka-World, and more specifically in the RobCo Battlezone. Additionally two can be found on pillars guarding the entrance outside. Instead of a claw, a space laser replaces one of the hands.
The Novatron eliminator is an upgraded version of the Novatron, the Nuka-World variation of the assaultron. The Novatron eliminator is the strongest variation of the Novatron and assaultron, and can be found in the RobCo Battlezone, in the Galactic Zone of Nuka-World.
Despite both the assaultron and the male Sole Survivor being affiliated with the military, the latter's dialogue choices with KL-E-0 would imply no prior knowledge of the assaultron model robots (although it is possible that the assaultron entered service with the US military after he had been discharged or they may have not been deployed to the front lines). This would be consistent with their absence in the Fallout 3 add-on Operation Anchorage.
If the assaultron is being attacked by two enemies at once (e.g. synth relay grenade) and the NPC is targeted, if the Sole Survivor is too close to the head/laser while the assaultron is firing, the player still takes massive AoE damage.
It is possible that assaultrons can express a very limited degree of human emotion. In Reunions, when Dogmeat leads the Sole Survivor to the remains of a destroyed assaultron, it states that it cannot feel its legs, in a slightly panicked manner. In addition, assaultrons appear to be able to feel pain as evident by the quotes of the damaged assaultron found while tracking Kellogg.