Evil Dave, real name David Karloff, is an aspiring "evil-doer" who lives in the basement of his mother's house in Edgeville and reads EVIL-DOERS MONTHLY. He first appears in Shadow of the Storm as a member of an evil cult trying to resurrect the ancient demon, Agrith Naar. During this quest, he is in the basement of the temple ruins in Uzer.
It is possible to contact Evil Dave by using the spell NPC contact after the Dream Mentor quest. However he does not say anything important.
What you have to realise, Kaxo, is just how fragile little Davey is, and how the world can be a terrible, cruel place. I fear it just wouldn't understand him: Fluffy Pants Fridays for example, and the way he writes in caps, as if he's shouting.
So, I'm going to wait until he emerges from his dungeon, wide-eyed like a young faun, and takes some tentative steps into the world. Only he will know when that time is, and I'm sure it's not too far away.
Despite claiming to be "EVIL", he's actually a great guy. He can't stand violence (which makes him faint), or vandalism, such as someone filling in a crossword for him, which he views as "extreme vandalism". The whole town of Edgeville thinks very dearly of him and hopes the EVIL thing is just a phase. Some of his activities are chatting with his good friend Oziach about adventures, and conspiracy theories such as giant black knights and "dragon dragons", and helping Oziach with house repairs.
He is a member of the Lumbridge Secret Council. He was appointed purely because the Council must include a dark wizard and the other members did not wish to include somebody who could actually be dangerous. He is present when the Culinaromancer is freed in Recipe for Disaster and is subsequently frozen in time. He must be saved by feeding him his favourite dish, spicy stew.
Dave was once arrested for his evil-doings, much to his delight, but not even the arresting officer thought he was evil or could ever harm anyone. When he was arrested, he became very excited and confessed momentarily. The only evidence that was found were his fluffieduffies. In his cell, they became friends, exchanged stew recipes and they threw a stew party for the night shift. If the player chooses to defend, Dave will be very upset for being cleared, since that means he is not acknowledged of being TOTALLY EVIL.
The next year, he received an anonymous letter for Christmas, which gave him the feeling he was "in some SINISTER TEMPLAR CULT where we hang about in robes, eat dark chocolates and decide huge, world-changing things, like a NEW METRIC SYSTEM." Apparently not realising his identity was already known to the author for the letter had been addressed to him, he himself signed his reply "Evil 'X'". In the reply, which he wrote in his bed, he announced having written five letters to Zamorak, including his résumé, hoping for a job as his secretary.
Talking to Evil Dave while wearing clothing that is "evil" will get the comment "Hey, you're looking evil!" Talking to Evil Dave while wearing clothing that is "evil" and while having a hellcat out will get the comment "Hey, you're looking evil, and so's your cat!" Talking to Evil Dave while wearing several articles of clothing that are "evil" and having a hellcat out will get the comment "That outfit is TOTALLY EVIL! And you've got an evil cat too! To be honest, I'm a little bit scared of you!"
When contacting Dave by NPC Contact (using the 'random' command) one may tell him to "Build [one] an army worthy of Zamorak!" This is a reference to the 2001 film The Lord of the Rings: The Fellowship of the Ring, based on the works of Tolkien, wherein Sauron orders Saruman to "Build [him] an army worthy of Mordor!" through one of the seven Palantír.
During the opening cutscene of Recipe for Disaster, Evil Dave says that "These secret meetings are SATANIC!" in the French version of the game, referring to the Satan, or Adversary, from the real-life Old Testament. On English servers, however, he simply calls the meetings "SOOO EVIL!"
His name is a possible reference to William Henry Pratt, better known as Boris Karloff, who was a notorious English actor, famous for his classic roles in horror movies.