Gundyr

Gundyr, also known as Iudex Gundyr and before that Champion Gundyr was a knight who was once destined to become a Lord of Cinder.
Gundyrs true origin is unknown, but what is known is that at some point he set out on a quest to destroy what was known as Aldrich's deep sea, promising that he would be back to Lothric Castle and the Firelink Shrine and that he would become the next Lord of Cinder, in a time of great uncertainty as to who would succeed Prince Lothric. Before his journey he was also assigned his own Firekeeper who he swore to that he would return, before being gifted the Coiled Sword of Firelink to show how his journey was one for a Lord. Gundyr then left Lothric Castle and travelled to the Cathedral of the Deep where the Deep Sea was located. When Gundyr arrived he noticed the Deep Sea was giving off a strong aura and without thinking of the consequences, Gundyr leapt into the sea to attempt to destroy the main forces that were controlling the aura.
For days, Gundyr destroyed countless amounts of abominations in his attempt to quell the darkness, but the Deep Sea began to have an effect on him. Realising that his time was running out, he slew as many as he could and attempted to try and escape. That was when a great beast appeared before him and began to drag him back into the Deep Sea and as such his exposure was longer than he anticipated, but slay the beast he did and then clawed his way out. By that point it was night time and he began his long journey back to Lothric Castle, until he realised that after several days of travelling, it was not night at all, but rather there was simply no light at all, yet his vision was still somehow not impaired, if not heightened by the lack of light. 
As he arrived back at Lothric Castle, it appeared to be completely abandoned and when he got to Firelink Shrine, the darkness persisted and discovered the body of his firekeeper, who had gouged her own eyes out at the sight that the world had become. Realising that he had broken his promise and his vow to become Lord of Cinder now in ruins he began to become extremely mournful and yet filled with rage. Only then did he notice a stranger, later revealed to be the Ashen One and thinking that he had something to do with this, attacked him. The duel he fought with the Ashen One was quick and lost the fight was relative ease, officially dying after being impaled by his own Coiled Sword. 
Through some form of Universal Paradox, the state of Gundyr transcended time and as a result appeared within the Cemetery of Ash, coiled sword still imbedded within him but none could remove it from him. This in turn led to a prophecy that the one who would wake Gundyr and remove the coiled sword would also be the one to become the next Lord of Cinder. Strangely this person was indeed the Ashen One, being woken up in 1695FY and slain, which of course then led the Ashen One to become the next Lord of Cinder, but instead letting the flame fade for the First Time in history after using the eyes of Gundyr's firekeeper to show his own firekeeper that they could live in a darkened world. Due to this paradox, there is no true way of knowing which of these deaths came first, but its likely that Gundyr's darkened world came first in 1683FY, despite actually happening in 1698FY, but ultimately leading to his last death in 1695FY yet technically his second death.