Drezel is a monk who lives in the passage bordering Morytania and the forest east of Varrock, under Paterdomus. He is heavily involved with the Priest in Peril quest, where you must help him escape from jail, and once that is completed, players can talk to him to start the Nature Spirit quest.
Drezel is the solution to the medium cipher clue: GUHCHO. The answer to his challenge: Please solve this for x: 7x - 28 = 21 is 7. Note: Only partial completion of this quest is needed to finish this clue. You must kill the guardian and get the golden key to free him. Talk to him in the passage and not the cell to get the challenge clue.