Comments posted to our Dark Souls 3 Wiki
it's an Alaskan Bull Worm
I was cheezing the sandworm today, but this time he turned around and started shooting lightning everywhere
Solaire is carthus sandworm!
how much HP does it have?
It's implied it could be Solaire but a Sunlight Maggot wouldn't transform him into what is seemingly a Chaos Demon/Centipede. Not to mention Canon doesn't have Solaire dying, his gear was well taken care of. Probably left over assets. Probably a poor attempt to tie in the Miracle, the unused asset and remove the Arch Peak Boss ties to Solaire.
Edit; I doubled checked and the Lightning Stake makes no mention of Solaire/Sunbros and even predates him. Nameless is more likely to be Solaire.
Or maybe solaire isn't represented as anything in the game other than his Armor sword and covenant