Pox is a cat belonging to Hooknosed Jack, a strange man located outside the Dancing Donkey Inn in south-eastern Varrock.
During the Ratcatchers quest, the players must poison a wedge of cheese in order to kill some rats. However, Pox ended up eating one of the rats, which in turn, made him sick. The dilemma is then solved by obtaining some Cat antipoison and using it on Pox.
He is found by the manhole close to Hooknosed Jack in Varrock, and inside the warehouse full of rats during the quest.
His name is a reference to the disease, Pox, which is often caused by viruses found in animals.
He looks slightly different when hunting rats inside the warehouse to how he looks when with Jack.