In my studying of the Dark Souls lore spanning the three entries in the series, I've recognized that pretty much everything we're presented with can be interpreted allegorically, and I've developed a fairly thorough thesis on the allegorical symbolism of the first two Dark Souls games. Please note that this is merely my interpretation based on the lore of the Dark Souls series, and I hope you at least take it into consideration when shaping your own interpretations of Dark Souls.
As a recap,
Dark Souls 1
tells a story of the desires of any ordinary individual to overcome "The Curse", an affliction that necessitates the suffering of all living things. To suffer is to slowly lose hope, and to lose all hope is to "Hollow" and become husks of our former selves. We're told that we may defeat this curse by embarking on a journey through the land of Lordran and by ascending to the very source of the curse, that through this arduous action we will find freedom from "The Curse", freedom from life's suffering. However, despite the seemingly inherently conflicting choices we're presented with from the mouths of serpents, we realize the ultimate truth: We never had a choice to begin with. The only way to truly escape "The Curse", the only way to truly escape life's suffering, is through death. As our body burns, we realize that all we've accomplished is the continuing of an endless cycle.
Dark Souls 2
we arrive in the land of Drangleic only to find ourselves in quite familiar circumstances. Embark on a journey to seek the king of this land, overcome various trials and tribulations, and if successful you shall find freedom from "The Curse" … or at least, so they say. However, this time we are not subject to two serpents separately trying to whisper their wills into our ears, but instead we're met by a single being who simply posits points of consideration onto us. What drives us? What is it we desire? Perhaps what we desire is but a falsehood, an illusion. And yet, is it so wrong to bask in blissful ignorance, to desire such happy illusion in such a cold world? But what if there is more? What if there is a true freedom from "The Curse", a freedom from life's suffering that doesn't necessitate our own death? What if there is a way to break the cycle, a path to enlightenment that might undo our curse for good? With these thoughts in mind, we eventually find ourselves confronted by the same choice we made before. This time though, we know better. There was never a choice to begin with, and we are but slaves to the cycle of light and dark. So we carry onward, rejecting the false freedom presented to us in favor of pursuing a more tangible remedy to "The Curse". As beings of dark, we ceaselessly pursue possibilities beyond ourselves, seeking a true freedom from the curse if such a thing even exists. Ignorant of what might lie ahead, we nevertheless carry on. Such is our fate.
Dark Souls 3
we are brought back to witness as the fire looms dangerously close to fading, and the distortion of time and space that ensues from this event. But we begin our journey as failures. In being The Ashen One, it means we previously failed in our duty to link the fire and have been reduced to ash. We are the lowest of low, and yet in our pitiful state we are free from "The Curse" and free from the effects of hollowing, as if our failures have groomed us into more resilient beings more capable of standing strong against hardship. The world around us is in turmoil, competing religious factions seek dominance while the darkest aspects of man are running rampant, and yet in our pitifully ashen state we are special. The Ashen One is a symbol of free will and choice. One who has endured hardship, rejected falsehoods, refused to beaten down, and has retained hope through it all. Through our experiences we now truly decide the fate of the universe we're presented with in Dark Souls 3. The final foe that stands against us represents everything we are not, everything we wish we were. The Soul of Cinder is an amalgamation of everyone who has previously succeeded in their duties and ascended into greatness. The Soul of Cinder is our desires manifest, and by conquering our desires we are now free to choose: Light the flame, Let it fade, Stamp it out, or Perhaps allow it to serve the age of man. Regardless of what we choose, every hardship we've endured to get here, every challenge we've overcome, every moment of success and anguish throughout our journeys, and every sense of meaning we might have carved out of the meaningless, after three full Dark Souls games we can say that we have shown ourselves and earned our right to choose.