Memble is a gnome in Gwydion Forest. He isn't there when you first walk through Gwydion Forest, he appears first after you exit Blackwhisper Cave and will stand there when you walk through on your way to Bavelock.

If you talk to him he will tell you about his sick wife. In the sidequest "Gnome trouble" you help him find the Wisp necklace that he hopes will help her wife.