So I was watching one of those Iceberg videos and stumbled across one for Dark Souls 2 and it reminded me of my big Pet Peeve for the Souls Sequels: Orestein basically becoming Boba Fett. So basically one of the big Bosses in Dark Souls is Ornstein and Smough, who are the big Boss of Anor Londo and the transition to the last 3rd of the game. It's a big thrilling Dual Boss battle and a fan favorite.
So in Dark Souls 2, you meet a boss who looks very much like Orestein called "The Old Dragonslayer" and he's hinted that he might be Orestein. While it's unclear if he is Orestein or not, he's clearly there to appeal to fan nostalgia for Orestein because there's no other reason for him to be there.
Dark Souls 3 takes it a step further by actively retconning that he never died and left Anor Londo, Leaving Smough to be the last "Knight" guarding the Cathedral and you eventually find his armor at ArchDragon Peak. Except in DS1 it's clearly stated Smough wasn't allowed to be a Knight, unlike his comrade in arms Orestein, so we're apparently retconning that too.
So much like Boba Fett, he was killed and then returns much much later because fans really, really like him, despite there being no good reason. Some fans try to handwave this that the O+S in Anor Londo are Illusionary much like the Princess, there's no proof this was the case in Dark Souls. The fact you get a Named Soul when you kill them, like every other boss in the game, supports this. And as much as I like Dark Souls 3, this irritates me FROM just tries to retcon this because the fans love the guy in the cool armor and they're gonna bring him back no matter how little sense it fucking makes. The only other way to explain it is basically that time is really messed up in Lothric due to all the fun fire dying stuff so you're basically seeing alternate timelines that previously didn't happen, much like whatever the fuck is going on with the untended graves.
Nobody else in the Souls games gets this treatment. Artorias has his fan club the Abyss Watchers and while some of his essence may flow within them he doesn't flat out come back because fanservice, the Great Souls in Dark Souls 2 are reincarnations of the Lords from DS1, not flat out just returning and the Soul of Cinder is basically a composite of every fire linker. Ornstein has cool armor and.....well, he has really cool armor and a thrilling battle and that's apparently why the fans love him enough to warrant messing around with the lore in this manner.