Set in present day Egypt, a race of immortal humanoid beings were seen with a translucent body armour covering from head to toe. They come in peace and harbour no ill intents, that said their kind of see through armour looks intimidating but the alien claims to be immortal and do not need to breathe. Why would immortal being needs armour that are translucent and covers the entire body? Kindly focus on armour itself and refrain from adding any additional non essential features such as antenna and jetpack, etc. These immortals can experience pain but they can still easily make a sound judgment or decision despite suffering from intense pain both mentally and physically, they are not just biologically immortal but also virtually immortal as in they could transfer their mind into one of many backup clones at almost speed of light.

• It keeps the wind off my skin


• It's fashionable and sexy


• Wearing the most expensive armour makes my neighbours jealous


• It has pockets!


• If some ape barbarian cuts my tentacle off with a sword, it really itches while it grows back, that happened to my great-grandfather you know


• If an ape shoots me in the primary nerve cluster with a shotgun, my brain will grow back but some of my memories and skills might not


• This armour belonged to my great-grandfather, I am proud of my heritage, and I will not be drawn into a discussion about whether he "came in peace" or "owned ape-barbarian slaves" before the galactic civil war

Degrees of Immortality

There are different degrees of immortality. Sure, your alien doesn't need to eat, sleep, or breathe. He(?) does not age. But that doesn't mean that there are not other things that can kill him. Maybe he can still get sick, especially on an unknown planet. Or maybe illness is out, but he can be killed by a rock over the head or a knife through the heart. So he has armor to protect himself from the things that can end this lesser degree of immortality.

Or maybe he has a higher grade of immortality, and nothing can kill him. He might still feel pain. Heck, he might be able to get sick, it's just annoying and inconvenient, never lethal. He might be able to be injured, he just always recovered. Or even even if he can't be cut or crushed, that might still hurt him

Even if none of that is true, he is still a corporeal being. He can be trapped, tied up, buried alive. Which leads too...

The armor does more

The armor might be about more than protection. It could have high-tech translucent tools built in. Scanners, an artificial musculature, laser cutters, etc. Tools he might need to help the populace, or to escape them.

He's Lying

It's not translucent armor. It's a hologram or something similar, that makes it look like that. In reality, the alien is hiding his hideous natural form, or battle suit bristling with weapons. Or both EXTERMINATE

It’s not there to protect the alien, it’s there to protect you. Aliens are hideously toxic/made of self-replicating nano-bots/highly radioactive/give off a constant really annoying sound/smell really bad and they don’t want to expose humans to it. Not after what happened at the last place anyway...

Oxygen

Oxygen is critical for life on earth but it's also the reason we age. One of the best selling categories of supplements at health food shops is anti-oxidants which claim to get rid of oxygen 'free radicals' from your body so as to limit the damage that they cause.

It's also one of the reasons that trees and other plants release the excess oxygen from photosynthesis into the atmosphere; it's toxic beyond the level you need to metabolise for life, so why store it? That's only going to create other problems.

So; your alien may well be immortal, but if he is then it's probably because he doesn't metabolise oxygen anymore, but fuels his body's metabolism through some other energy model. He might even be photovoltaic; that is to say, generates the electricity to power his own nervous system and muscles directly from sunlight which is why the armour is translucent, but he needs it to be airtight to seal him out of an oxygen rich environment to preserve his immortality and stop his body from aging by reacting to the oxygen.

That way, you have both covered. His armour is really a spacesuit that keeps an inert atmosphere around him, and it's translucent so he can harness the light energy from the sun to power his immortal metabolism without resorting to a chemical energy based model.

These immortals are made from anti-matter

With the help of the translucent armor, they can create dashes of antimatter when needed, just to create a small fireworks, BUT with the help also of the armor, they don't explode. Once the armor is remove, they too, along with us, vanish...

Let's see,the armour being translucent would be creepy. As all you'd see beyond is the vague colour and mass of the aliens without proper identifying features. However it hiding identifying features can be very different for us and the aliens. For instance if the aliens identify one another by various light and colour patterns via bio-luminescence for example they would not need to see clear shapes. Especially if the aliens in question were formed largely of:

1. Energy,so they use the armour as a means of interaction with the physical realm in more meaningful ways. Thus allowing them to physically touch and manipulate objects; while also giving humanity a more relateable form to interact with.

2.Were so mind bending to look at without the barrier of their armour (whether incredibly beautiful, unspeakably hideous or simply something that causes human cognitive functions to go haywire) they need it to obscure their true form.

Another alternative is this can give more mundane advantages. It allows the aliens more leeway in who can go to diplomatic meetings. If they sound similar and all (to us) act similar, they could all claim to be High Elder Karth for example and we'd never know as we can't actually see them. That makes diplomacy more cautious and can favour them in that way. Additionally armour is just a good idea. You may be immortal (whether biologically immune to disease or age,have multiple bodies,be present mainly in higher dimensions,etc) but that doesn't mean your body used for interaction is.

The body might just be a shell for their consciousness which needs time to reform a new body. In your case however I'd say the aliens are likely beings who rely upon colour patterns discerned in one another to know identity and communicate. Hence in their culture opaque armour would be seen almost as extremely asocial behaviour. Shutting oneself off utterly from others of their species could be one view.

The other is that opaque armour is worn to hide ones identity. Commonly associated with criminals and possibly the military. In a society so based around open communication and via visual colour based cues it'd be very hard to trust someone who exhibits none of those characteristics. The one thing these people fear more than anything is members of their kind who wish others of their kind ill.

So maybe, they see the armour as not intimidating but to us it is frankly quite the opposite. They are wearing the armour simply to give themselves a solid form that also protects them against the few things they are vulnerable too. While they are also wearing the armour because they can't help but worry what these strange opaque creatures who communicate via vocal language and physical movement will be capable of.

Just my thoughts on it.