Gnarl is one of 2 half-ogres guarding bridge leading to the Gnoll Stronghold. He will demand a payment of 200 gp to let the party cross the bridge. The price can be negotiated down to 100 gp.
Gorion's Ward can also refuse to pay and initiate combat. This is the recommended path, as killing Gnarl and his companion Hairtooth is the only way to obtain the Gauntlets of Dexterity.