Earl was orphaned at an early age, and became a dock rat. By the time he turned 12, he had joined a gang called the Northside Ne'er-do-wells; by the age of 16, he was their leader. Their main rivals were a gang called the Southside Scallywags, led by Seamus. In 890, Seamus started talks with Earl to unite the two gangs, which would make them both more powerful. Most of the Ne'er-do-wells were in favor of the idea, and Earl saw that it was in their best interests. So, he agreed, but then immediately retired from the new gang, which was called the BiShip Brigands (which would, some years later, be led by Jack Dockrat, who merged the Brigands with the Cosa Nostra of Shipsister to form the inter-village gang BiShip). Seamus became the first leader of the Brigands, but Earl was no longer interested in being in a gang. He had always enjoyed a good fight, and with no real enemies left (aside from the police, of course), he was ready to look for a new lifestyle, which could provide him with more opportunities for fighting and adventure.
So, at the age of 19, he joined the crew of a pirate ship, the Kaizoku Jidai, under Captain Okami. He worked quite hard to learn all he could about sailing, and to prove his worth as a pirate. By age 26, he had become first mate; and when Okami retired in 900, Earl became the ship's new captain, at age 29.
It was in 892 that the Kaizoku Jidai first faced off against Reginald of Port, captain of the Victory. At the time, Earl was still a junior member of the crew, but he played an important role in the battle. While the details are unclear, it is said that he not only helped his crew best that of the enemy, but he also saved the life of Reginald's niece, Helen, who was a passenger on the Victory at the time the pirates attacked. She became a hostage of the pirates, and subsequently fell in love with Earl, whom she married in early 893. Later that same year, they had a son, whom they named Mark. Helen left her wealthy clan to live in Ship, along with Mark; Earl would see them as often as he could, though the pirate's life often kept him away from home for long stretches of time.
When he did visit his wife and son, he often regaled them with stories of his adventures. It's said that when Mark was about six years old, he responded to one of his father's stories by saying "That's awfully dark, father. But I like it." This anecdote is often used to explain the fact that, when Earl became captain a year or two later, he renamed the ship Darkfather. However, it should be noted that the ship's former name, Kaizoku Jidai, means "Pirate Era" in a language from Earth. The first great pirate era on The Land had been centuries earlier, between roughly 362 and 379. Okami had given his ship the name he did because he hoped to play a part in establishing a second great wave of piracy. In spite of being generally recognized as the greatest pirate of his own time, this new era never quite manifested. But in spite of changing the name of the ship, Earl promised to do his best to continue working towards Okami's dream. And in fact, Earl himself is credited with/blamed for doing just that; the second wave of piracy began in the early 900s, not long after he began his tenure as captain of the Darkfather. (While there are many tales of his exploits, perhaps the most famous are of his occasional confrontations with the Victory, following in the tradition of Okami. In the same year Earl became captain of the Darkfather, Reginald's son, Althis- Helen's cousin- became captain of the Victory.)
In 903, during the Coming of the Order, Earl and his crew fought on the side of the Protestant Movement, but returned to a life of piracy immediately after the war. Also during the war, Althis joined the Navy, at which point his cousin, Sebastian- Helen's brother- became the new captain of the Victory. The rivalry between the two ships continued, as did the self-imposed prohibition (first by Okami and later by Earl) against killing any of Helen's clan.
In 904, when the surname law was passed, Earl chose the name "Prowess," a boastful name based on his skill as a sailor, fighter, and captain. (Few people if any, even among his enemies, consider this name truly arrogant, as he clearly earned it.)
In 912, Earl and his crew fought in the Chaos War, on the side of the Chaos Navy. However, while several pirate ships subsequently became part of the full-time navy of the United Villages of the Chaos (thus abandoning a life of crime in favor of legitimacy), the crew of the Darkfather chose to return to piracy after the war. (The Darkfather, before being captured by Okami and named Kaizoku Jidai, had been known as the Java Junk III. During the war of 903, the Darkfather had fought on the side opposite that of the next ship in the same line, the Java Junk IV. But in 912, it fought on the same side as the Java Junk V.)