Bylvis is a rancher located at Katoa Ranch. He is a villager NPC that owns an underground ranch, which is visited during Tunnel Trouble to free the cows.
Prior to the 1.17 Dungeons and Discoveries Update, Bylvis was the starting NPC for the quest A Confused Farmer.
In A Confused Farmer, Bylvis seems to have succumbed to alcoholism, due to the fact he mistook Drale for a cow for a long period of time and mentioned Nemract Whiskey.