Jack spent his entire childhood as a dock rat, and while there are no records of his family, it is believed his parents were also dock rats. At age 14, in 894, Jack joined a local gang called the BiShip Brigands, which had been created four years earlier by the merger of two smaller gangs, the Northside Ne'er-do-wells and the Southside Scallywags. The Brigands were led by a young man named Seamus, who had previously been the leader of the Scallywags. Less than a year after Jack joined the gang, Seamus retired, and was replaced by a 17-year-old girl named Deirdre, who had been with the gang for four years.
It was five years after Jack joined the Brigands that various inter-village gangs began to form, in 899, most notably LandOrder and InterGang. At that time, the Brigands remained independent, but the changes to the nature of gangs in other villages made Deirdre begin to realize her own gang would have to become more serious, if it was to survive in the new era of organized crime. She did her best to adapt, but by 903, she realized she simply wasn't interested in continuing to live as a gangster. In her day, it had been a kids' game, and she was no longer a kid. But in the years since she'd taken over the gang, she'd naturally gotten to know all her fellow gangsters quite well. She saw in Jack a natural ability to lead the gang the way gangs were led, these days. So she retired as leader, passing her position to him, and encouraged him to see if either LandOrder or InterGang would be interested in acquiring the Brigands as a new branch of their organization. Jack became the first leader of the Brigands to call himself a 'don,' as the branch leaders of the larger gangs had done since 899.
It was around the same time that Jack became don of the Brigands in 903, that Milo, don of the most prominent gang in Shipsister, the Cosa Nostra, was also seeking to join one of the inter-village gangs. It's unclear how much progress had been made in these efforts by either Jack or Milo, when the Laser Plot took place in Ship in early 904. This made police as well as the Coast Guard more vigilant particularly in Ship, but also all port villages, including Shipsister. Whatever interest the larger gangs may have had in those villages quickly dissipated. This is apparently what led Jack and Milo to start their own two-village gang, BiShip. The union would prove beneficial to both gangs, in the following years.
Later in 904, when the surname law was passed, Jack chose the name 'Dockrat,' for obvious reasons. In fact, most 'rats around the world began calling themselves by their specific type: Dockrat, Streetrat, etc., rather than choosing an actual family name. Meanwhile, Milo chose the surname 'Longshore.'
In 912, Tiejo Streetrat joined a group of would-be rebels called The Chaos, and secretly began asking friends of his in the 'rat communities of any villages the Chaos went to if they could organize their friends into a potential army to assist the Chaos, when they were ready to make a move. The Chaos eventually decided against rebelling against the Second Order, but their actions nevertheless contributed to the Chaos War, later that year. A friend of Tiejo's named George Dockrat had begun organizing 'rats in Shipsister, which came to the attention of Milo Longshore. He talked with Jack Dockrat about organizing 'rats in Ship (though neither don wanted to commit their actual gangs to helping the Chaos). When the war finally began, the 'rats Jack had organized for the cause assisted a task force of merchant ships from other port villages by sabotaging the Navy base in Ship, during the Battles of East Ports.