Barão Alwin, also known as Baron Alwyn or Lord Alwine, serves as the primary antagonist in the anime. He holds the position of Baron of Nottingham, a station of power and authority he uses to oppress the region's inhabitants. His background is rooted in a deep-seated greed and a desire for total control over the county. Years before the main events of the story, he was responsible for forcing a young man who would later be known as Little John and his friends into brutal forced labor, ultimately driving them to seek refuge in Sherwood Forest. His cruelty culminated in his most infamous act: ordering the complete destruction of the Huntington family's castle, an event that orphaned the protagonist, Robin, and his cousins, forcing them to flee for their lives.

In terms of personality, the baron is defined by his cruelty, greed, and inconsiderate nature. He is a calculating and ruthless nobleman who views the common people and even lower-ranking nobles as mere tools to be exploited for his own enrichment. His primary motivation is to increase his own power and wealth. This manifests in his heavy taxation of the poor and his relentless pursuit of Marian Lancaster. He seeks to have her adopted by his accomplice, the shady Bishop Herfort, in a scheme to seize the Lancaster family's hidden fortune, which is tied to a secret carved into a cross that Marian wears. His goal is not simply to eliminate Robin and his band of outlaws, but to crush any resistance to his oppressive rule over Nottingham.

Barão Alwin’s role in the story is that of the central villain whose actions drive the plot forward. He is the direct cause of the protagonists' suffering and the reason they live as outlaws. Throughout the series, he commands his troops, led by the dangerous knight Gilbert and later by the mercenary Guy of Gisborne, to hunt down Robin and his friends, destroy their hideout, and recapture Marian. His position puts him in direct conflict with Robin Hood, Little John, and Friar Tuck, making him the primary obstacle the heroes must overcome. His key relationships are defined by his power and malice. He is the master of Gilbert and his soldiers, and a partner in crime to Bishop Herfort. His most significant relationship is his adversarial one with Robin Hood, whose constant acts of defiance and thwarting of his plans become a personal obsession for the baron.

Despite his seemingly one-dimensional villainy, Barão Alwin exhibits a notable development over the course of the series. After suffering repeated humiliations and a near-death experience at Robin’s hands, he begins to show signs of a genuine change for the better. For a time, he appears to reconsider his cruel ways. However, this redemption is short-lived. He soon uncovers a plot that could allow him to take over the entire kingdom, and the temptation of this ultimate power proves too strong, reverting him back to his original greedy and inconsiderate self. This relapse leads to a final confrontation in which his scheme is ultimately foiled by Robin Hood and the intervention of King Richard himself. As a nobleman with significant resources, his notable abilities lie not in personal combat prowess, but in his authority, wealth, and strategic command. He controls a formidable army of soldiers and has the financial power to hire ruthless mercenaries, making him a dangerous enemy through his influence and resources rather than his own physical strength.