Lonesome Gavlan is the last of the truly sane Gyrm, making him the last of his kind. He is located in No-Man's Wharf, Lower Eathern Peak, and the caves below Blightstone Cave Tseldora. A Gyrm sat usually next to a chest, drinking an ale of sorts, he seems to be non-hostile to the player, even though his race has a great vendetta with the humans of Majula.
Gavlan is a merchant, as such, he sells you items, mainly items that afflict poison on impact or that cure poison.
Gavlan is one of the only NPC's that you can sell to. With the exception of a handful of items, you can sell him any item that you view as junk.
Much like any character in the Souls games, the player can fight and/or kill Gavlan, in which case he drops a Gyrm greataxe if you defeat him.