Jack the First is the Jack from the original and controversial story of "Jack and the Beanstalk". He is usually portrayed as the hero, and it is made sure by always portraying the giant as the villain. On the other hand, it is Jack who's the real villain, though this is unintentional. He is just trying to make his mother proud.
According to Jack and the Beanstalk: The Real Story, he is the ancestor of the same-named protagonist Jack Robinson. In an attempt to complete his goal, he greedily betrayed the kind and friendly Thunderdell's warm hospitality and friendship and stole the goose that laid the golden eggs and the magic singing harp and killed the giant for attempting to save the gifts. It is because of this that his descendants, about to end with Jack Robinson (which is why Sigfried Manheim, Jack's boss, encouraged him to care only about his work and never marry, and it is so that he could take over the company), never lived to be over 40. This Jack is played by J.J. Field.