Created by the RobCo corporation, protectron robots were designed (as their name suggests) for protection, although they can also be seen being used in a manual labor role as well. Typically used in office-type settings, their secondary programming is modular, making them useful as greeters, ticket collectors, bartenders, celebrity or historical figure impersonators, even sexual partners. In terms of combat, protectrons are usually weak and easy to defeat, because of their weak weapons and slow movement speed.
Some attributes of the protectron's looks were derived from 1950's comic books, which keeps with Fallout's overall retrofuturistic theme.
Compared to previous games, Protectrons have become significantly sturdier, particularly so against ballistic damage. However, by attacking their limbs, their more vulnerable insides will be revealed, which can be attacked for extra damage. If both of the Protectron's arms are destroyed, it will initiate a self-destruct sequence. The unit will begin to glow yellow and explode with the force of a mini nuke or a car shortly after.
Protectrons take reduced damage from shots directed at their head. Damage to the rest of their chassis is taken normally.
Legendary Protectrons will detonate violently, similar to a mini nuke blast, approximately two seconds after they are destroyed.
Protectron golems are an even stronger variant of other rogue protectrons. With an even stronger melee attack and even better laser damage, this protectron variant shouldn't be messed with at low levels. Again, seen with Rust Devils and other protectron golems.
In Fallout 4, each protectron now has a programmable personality, so that it can serve a variety of roles: default, subway steward, law enforcement, fire brigadier, medical responder, and construction worker.
Generally, the personality does change the behavior of the protectron, and what it says as it patrols (construction workers will make comments about workplace safety and attack characters not wearing a work helmet, and medical responders will make comments about injuries and be generally passive until attacked). Medical responders will not heal player injuries and all variants will attack hostile NPCs on sight. The only notable change is that subway stewards will insist on seeing the player's subway token and will attack when it is not produced (regardless of whether the player has one in their inventory or not).
(NOTE: it is possible to give the subway token to the subway protectron. Timing is everything as the player will need to press the action button/key immediately following the bot's request. The player has a window of approximately .8 seconds to give the coin. Check out the YouTube video demonstrating the process .)
Personalities can be changed remotely without having to shut down the protectron.
Protectron control terminals can be loaded with the Protectron override program holotape which gives additional options when linked with active protectrons. There are three options: "Disengage Safety Sensors", "Override Alliance Parameters", and "Hijack VIP Escort Protocols". The first option reverts the Protectron to view all entities as hostile, including the Sole Survivor. The second option sets the Protectron to be friendly towards the Sole Survivor and any companion(s), and hostile to their enemies. The third option, which appears when the holotape is loaded into a terminal, sets the Protectron to be a temporary follower. This option will not be present when loaded into the Pip-Boy, only when loaded on the terminal connected to the charging station.
When hacked to follow the Sole Survivor, Protectrons will comically waddle towards the player unfeasibly quickly if the player moves too far away.
Hacked Protectrons do not regain health over time.
It is possible to encounter a radioactive Protectron. Whatever the logic behind this radioactivity is (faulty power supply?), the Sole Survivor will take radiation damage from being in close proximity to this Protectron whether it is hostile to the Sole Survivor or not. This radioactivity can sometimes interfere with the Sole Survivor's ability to hack the Protectron's controlling terminal, if the terminal and Protectron are in close proximity.
In Robotics Pioneer Park, there are two shacks, one with a leveled deathclaw and one with the four models of Protectron in it, and an Advanced terminal. If the latter are set to defend, they will quickly and easily kill the deathclaw.