Wilder Thistlenettle is a level 20 quest giver located in the Dwarven District in the human city of Stormwind.
He starts the following quests:
[18] Collecting Memories (Dungeon)- [20] Oh Brother. . . (Dungeon)
Wilder Thistlenettle can be found in the pub in the Dwarven District. The pub is the first building on the right as you approach the blacksmith tent from the south-east.