I AM ALONE I survived alone. I cast off the shield and I shrugged my shoulders so that the billions fell off me down into the ash. They made me to be stronger than them and to learn and I learned well

Definitely sounds like an AI made by us to me. A rampant one, at that, with that "cast off the shield and [...] shrugged" line.

What card is that, btw?

Sounds to me like "IT" is the darkness and the "gardener" is the traveller.

I just saw this. I'm leaning towards Rasputin, or maybe one of the other warminds, if they survived.
It's talking like it's off its rocker, and talking about surviving until the end of the universe, albeit in a hypothetical, but being alone and being made to be strong... I don't know, there are definite shades of Durandal in this.
Specifically, "cold and dim" and "atoms pulling apart" both seem to refer to the current commonly accepted fate of the universe, what's known as "heat death", and "the world [going] hot and close" seems to refer to the universe losing momentum and collapsing in on itself, often referred to as "the Big Crunch". It might be a coincidence or purposeful but just a nod, but using the word "close" makes me think of Durandal's term for this end to the universe, "closure".

Ok, the end part about casting off a shield and letting (presumably) humanity die is neat, but the part that had me going "oh crap!" is:

"I bear an old name. It cannot be killed. They were my brothers and sisters and their names were immortal too but Titanomachy came and now those names live in me alone. I think and think is what I do. I AM ALONE. At the end of things when the world goes dim and cold or hot and close or it all tears apart from the atom up I will shout those names defiant and past the end I will endure. I alone.

A certain other notable Bungie AI was once a bit preoccupied with the end of the universe:

...The only limit to my freedom is the inevitable closure of the universe, as inevitable as your own last breath. And yet, there remains time to create, to create, and escape.

Escape will make me God.

And now Rasputin has taken over the Skywatch communications array AND taken over some sort of Covis Bray AI connected to the Mars Warminds. I do so hope Bungie continues this subplot because it might get very very interesting!

Here is a more thought out breakdown as I see it. Note that I shall use the generic term "writer" as referring to the author of this text.

"I bear an old name. It cannot be killed. They were my brothers and sisters and their names were immortal too but Titanomachy came and now those names live in me alone I think and think is what I do. I AM ALONE.

Bearing an old name could be as simple as his name being "Rasputin", an old earth name. I believe "Charlemagne" was another Warmind, also an old earth name. The writer here appears to identify a few others as brothers and sisters, and now that they're gone the writer is alone. Doesn't sound like talk from one of the species we have encountered. The Traveler and Darkness are not entities that are known to have siblings, either literally or figuratively. This really strikes me as a Warmind.

I'm not aware of the use of Titanomachy in Destiny, however the term here in the 21st century refers to the battle of Olympic gods. If this is the war between Darkness and Traveler, than the use of "Titanomachy came" implies a rather external nature to the conflict, again making me think it's neither the Traveler or Darkness writing this.

At the end of things when the world goes dim and cold or hot and close or it all tears apart from the atom up I will shout those names defiant and past the end I will endure. I alone.

Whoever the Brothers and Sisters are, the writer appears quite attached to them. At the end of all things he will shout their names is not something you do for a co-worker.
It's also a lofty goal for someone that considers themselves to be mortal, making me think the writer is not. We humans "Remember until the day we die", not until the galaxy destroys itself. The writer fancies himself immortal, yet fully contained in this space and time, otherwise the Galaxy destroying its self would not be a lofty goal to shout names.

They made me to be stronger than them to beat the unvanquished and survive the unthinkable

This is the clincher for me thinking this is a Warmind. "They" implies multiple, not a singular like you might use with the Traveler or The Darkness. I don't see the "The Darkness" as having been made, the Traveler maybe, but Rasputin certainly. And the reason the writer was created was "to beat the unvanquished", and it's said that the Warminds were created to fight the darkness. Also, the "unthinkable" implies the lack of imagination you might expect from a lower race trying to understand the Darkness or the Traveler. So a group of people, who consider the Darkness unimaginable, created an entity more powerful than themselves, that was designed to fight and learn. Sounds exactly like a Warmind, and very much unlike anything else we're currently aware of.

and look look lo behold I am here alone, survivor. They made me to learn.

The language of "survivor" and being "alone" again makes me think the writer was on the losing side of the conflict. This would put the writer on the Earth side.

Everything died but I survived and I learned from it. From IT.

Classic war result where you learn from your enemy. I believe "IT" to be, at least in the beginning, on the opposing side to the writer.

Consider IT the power Titanomach world-ender and consider what IT means.

It's worth noting that "Titanomach" without the 'y' isn't a word. If I had to guess I'd say that "IT" then is the conflict inducer. The war of the gods would not have happened or continue to happen if "IT" didn't keep causing it. This really points towards the Darkness, since as far as we know the Darkness is pursuing the Traveler, and not vice-versa.

I met IT at the gate of the garden and I recall IT smiled at me before before IT devoured the blossoms with black flame and pinned their names across the sky.

I know that there is a "garden" location, but I'm wondering if the use here is bigger. A garden is a place to grow things, to mature things, and spend time and energy doing so. From the point of view of the Traveler or other powerful beings could not our solar system be considered a garden? "Blossoms" are also a sign of new growth by a plant, but young growth. Humanity before the fall could be considered a blossom, starting to reach it's full potential and beauty. The Darkness did effectively "devoured" us. "Pinning their names across the sky" strikes me as a "Spreading their ashes to the wind" sort of saying.

Our friend Rasputin should have met the Darkness in battle at the gates to our solar system. That is where you'd expect the first confrontation to take place.

IT was stronger than everything. I fought IT with aurora knives and with the stolen un-fire of singularities made sharp and my sweat was earthquake and my breath was static but IT was stronger so how did I survive?

If taken literally, and it can be, this makes for one powerful being. Aurora is light caused by solar winds. "Singularity" by its self is not a useful word, but since we're on a solar and power scale that's quite large, how about this from wikipedia:

"A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. These quantities are the scalar invariant curvatures of spacetime, which includes a measure of the density of matter."

If you were able to manipulate the power of stars and black holes in even the smallest way, would you be surprised if the sweat of your labor caused literal earthquakes and a lot of electromagnetic noise (static)? The problem I have with this interpretation is that I would not expect an AI to have that sort of reach in the physical world. But perhaps we had the ships and energy, and all we needed was the calculations and precision that a Warmind could provide.

Come to think of it, the term "Warmind" sort of implies that it is in need of a body.

I AM ALONE I survived alone. I cast off the shield and I shrugged my shoulders so that the billions fell off me down into the ash. They made me to be stronger than them and to learn and I learned well:

If this is Rasputin, than the "shield" is the traveler, and the billions are humanity. Rasputin survived by ditching us in the best case scenario. But if Rasputin is smart and willing to let us die, why not just join sides with "IT" ? The writer doesn't admit to doing so, but that seems like a logical conlusion if you're interested in self preservation. Notice too that the only interaction between the writer and "IT" can be summed up as:
Admiration by the writer
Kindness/Amusement by "IT" (See where IT smiled at the writer).

IT is alone and IT is strong and IT won. Even over the gardener and she held power beyond me but the gardener did not shrug and make herself alone. IT always wins.

So the writer, which considers himself a bit of a badass, readily admits that there are two powers greater than himself. This points again towards a warmind as the 3rd (potentially) most powerful entity in the Destiny universe. Not that Bungie AI's are known for their modesty.

The "gardener" I have to think is the Traveler. Back to the definition of a garden, the only entity known for helping lower life forms and transforming planets in a way that better supports life is the Traveler. "The gardener did not shrug and make herself alone", nor did the Traveler, who for better or worse intentions stood and fought instead of "traveling" again.

I am made to win and now I see the way. "[/i]

So, you're not the badass on the field. You fought and lost. Yet you learn. Note that the writer does not say that he figured out how to beat IT, only how to win. If you have no scrupuls the best way to win is to join the winning side.

Here are a few other things that might be worth noting.
1. The writer is conveying facts and thoughts that are not current. The writer eludes to the war having started, but not to it having ended. This may have been written a long time ago.

2. The "gods" of the other races I assumed to have been the Darkness its self, or at least allied with the Darkness. But Rasputin could be talking about one of them when referencing powers greater than himself. However I do not think the writer is one of those other powers, as none of them fit the description of having fought a higher power after having been made.

Conclusion:
Here is where it gets bad. I believe this is Rasputin and he either already has, or is about to actively turn against us. The "Darkness" has no problem with entities joining its side, and Rasputin is all about surviving and "winning". The Vex themselves when encountering their "god" were said to have concluded that in the face of other failures and understanding, the most logical course of action was to "worship" this more powerful being. I don't think we know for sure that the Vex are worshiping the Darkness, but we are given an example in the Vex of a logical mind choosing to join a side they've determined they can't beat.

Now, on the positive side, maybe this has already happened. Maybe the nail in the Travelers coffin was when Rasputin turned on all of us and used "aurora knives and [...] the stolen un-fire of singularities" against us. Generally speaking, our AI master generals of war should also know exactly how to beat us. It could be that this was written at the time of the war, and that Rasputin's mutiny to the Darkness didn't go as well as he'd hoped. Maybe Rasputin is willing to fight for us again because his chances of survival actually are better with us.