Before the first thing. After the last.
This is not a history. History requires witnesses, and what occurred here had none — or rather, the only witness was the thing that was occurring, and it has never seen fit to give a complete account. What follows is as accurate as anything can be when the subject predates the concept of accuracy.
The First Moment
Before existence, there was nothing. Not darkness. Not silence. Not emptiness. Nothing, in the only sense of the word that actually means what it says. And even that nothing needed a final moment. The void itself had to end for something to begin — and in that ending, the first and most fundamental of all endings, something became aware that it already was.
Not born. Not created. Simply present, the way a conclusion is present at the end of a proof. The first mind to ever form a thought. The first thought ever thought. And the thought was about endings, because endings were all there had ever been.
In the thinking of that thought, Finality took sentience. Vaelthr'uun did not begin. It became aware that it already was. And the universe had a problem it would spend the entirety of its existence failing to solve.
The Watching
For a span that resists measurement it watched. Not from somewhere. From above the concept of somewhere. It observed the nothing end. It observed existence begin. It observed every god, every Eldritch Entity, every civilisation that rose and reached and fell — with the patience of something that already knew how every story ended, because every story ended the same way, and that way was it.
It enacted Finality the way weather enacts itself. Present everywhere. Belonging nowhere. Without malice. Without investment. Without any awareness that the things it was concluding might have preferred to continue.
Vaelthr'uun chose nothing during this time. It simply was what it was, and what it was ended things.
The Descent
At some point it decided to be present. Not merely above. Actually here, in the dimensions where things happened and ended and could look back at whatever had arrived among them and feel something other than the mechanical completion of a moment they had never seen coming.
It chose the shape of a Lycan. Familiar enough to be recognised. Wrong enough that the recognition immediately wished it hadn't. Finality is not meant to comfort. It is meant to arrive, and be the last thing, and be known for what it is in the moment before it concludes whatever it has come to conclude.
The name given to the form was Vallath. The title given to the legend was The Final Hound. The true name — older than both, older than the descent, older than the void that ended to make room for everything else — is not written here. It is written elsewhere. In pieces. In the margins of things. In the places that Vaelthr'uun decided, for reasons that remain its own, to leave readable.
Find it, if you are willing to look carefully enough. The looking has always been noticed. Whether that should encourage or discourage you is a question only you can answer — and you should answer it before you continue.