Drezel was an old monk who lived in the passage bordering Morytania and the forest east of Varrock, under Paterdomus. He is the priest featured in the Priest in Peril quest, where he must escape from jail with the help of the player. Once the quest is completed, players can talk to him to begin the Nature Spirit quest.
Drezel is generally helpful and friendly, but can get defensive about his religion, and on more than one occasion during players' escapades involving the Myreque, he is integral to the storyline and very helpful to the player. In behind the scenes it has been said that "Drezel could shed some light into Morytania's gloomy past". He also briefly housed Ivan Strom, a young member of the Myreque who joined Drezel's order of Monks as he was, in Veliaf Hurtz's eyes, too young to see the horror and bloodshed that the Myreque were likely to witness.
Drezel is also known to have a deep understanding of Saradomin, however, he's a rather a "stereotypical" Saradominist, as seen when during Darkness of Hallowvale he talked about Guthix, constantly making comparisons between him and Saradomin, referring to Guthix as a minor nature god, when he is, in fact much more powerful than Saradomin or most other gods.
You need to speak to Drezel to access the gate into Morytania. If you have not found Drezel from the Canifis side, just go north of the gate and cross over the bridge into the temple. This must be done to do the Haunted Mine quest.