Kruk is a monkey that is the head of the Ninja Monkey Guards of Marim, and is located on the east side of the gate, up on the hill. He is the monkey that shouts for the gates to be opened when you approach in monkey form. He is involved in the Monkey Madness quest, and players must talk to him before meeting King Awowogei to make an alliance with him. Although he has a combat level, he cannot be attacked, nor does he directly attack the player (he simply knocks the player out instead).
He also looks bigger than the other monkey ninjas. If you are caught wandering in Marim as a human, he will knock you out with the aid of his 2 guards and place you in the jail where you must escape. You can go to the cliff opposite of where Kruk is, there should be an opening there so you can walk up the hill. Next climb the ladder at the top of the cliff, cross the bridge and go down the other ladder.