Captain Nemo is the enigmatic and commanding captain of the Nautilus, a highly advanced submarine that serves as both a weapon and a sanctuary in the struggle against the Neo-Atlanteans. A middle-aged man of few words, he possesses a calm and taciturn demeanor that naturally projects authority, with his crew and allies often interpreting his reserved nature as a sign of immense charisma and unwavering determination. He has a tall, imposing presence, typically seen in a distinctive uniform, and is rarely seen without his signature mustache. Despite his stern and often stoic expression, he is capable of great warmth, such as when he offers a rare, kind smile in response to young Jean’s joy at seeing sunlight.

His true identity is Eleusis La Arwall, the rightful heir to the ancient and advanced civilization of Atlantis. Before the events of the series, he was the king of Tartessus, a hidden kingdom in central Africa that preserved Atlantean culture. His reign was defined by a significant ideological conflict with his trusted friend and prime minister, Gargoyle. Nemo, having witnessed the spread of humanity across the globe, believed that the remaining Atlanteans should seek peaceful coexistence with humankind. Gargoyle, in contrast, sought to use their superior technology to subjugate the world. This conflict culminated in a devastating coup led by Gargoyle, during which Nemo’s wife, the queen, was killed and his newborn daughter was lost. Nemo was forced to flee with a handful of loyal followers.

In a desperate act to prevent Gargoyle from using the Tower of Babel, a destructive Atlantean weapon, Nemo removed the controlling Blue Water, causing the tower to go berserk and utterly destroy the kingdom of Tartessus, reducing it to ruins. This tragic event, for which he carries a heavy burden of guilt, became the catalyst for his mission. He and his surviving crew, including a young orphaned girl named Electra, repurposed an ancient Atlantean spaceship into the submarine Nautilus. From this vessel, he wages a solitary war against Gargoyle and his reborn Neo-Atlantean empire, driven by a need to atone for his past and stop their ambitions of world domination. He is a tactical genius, capable of commanding the Nautilus in battle against entire enemy fleets and emerging victorious, a testament to both his ship's power and his own unflappable command.

Key relationships define his character arc. The most profound is his connection to Nadia, a young circus performer he discovers is his long-lost daughter. Upon learning her identity, his shock and subsequent actions reveal a deep, paternal love and a repeated desire to protect her. He becomes a mentor and father-figure not only to Nadia but also to the young inventor Jean, whose enthusiasm and brilliance he comes to respect. His relationship with his older son, the Emperor Neo, is one of tragedy, as the child was taken by Gargoyle, brainwashed, and used as a puppet ruler. He also shares a complex bond with Electra, whom he rescued from the ruins of Tartessus and raised; she serves as his fiercely loyal first mate. Despite his initial coldness, he also earns the romantic affection of the former antagonist Grandis Granva, though his focus remains on his mission.

Throughout the story, Nemo undergoes significant development. He begins as a mysterious and distant figure, motivated by a secret and sorrowful past. As the series progresses, the revelation of his history as a king and a father layers his character with immense pathos and regret. His cold exterior gradually cracks as he interacts with his daughter, showing a man burdened by loss but capable of profound kindness and sacrifice. In the final confrontation, after witnessing the death of his son and seeing Gargoyle defeated, Nemo sacrifices his own life. He overloads the Nautilus’s reactors to blast an escape route for Nadia and her friends from the collapsing Red Noah, meeting his end with his ship as a final act of atonement for the destruction of his kingdom.

Captain Nemo possesses several notable abilities beyond his skills in naval command and tactics. He is a brilliant scientist and engineer, having overseen the construction and maintenance of the Nautilus, which surpasses any contemporary technology. He is also a skilled musician, often retreating to his private cabin to play a hauntingly beautiful pipe organ, a piece of music that unconsciously draws Nadia to him. His decision-making is ruthlessly pragmatic, as demonstrated when he is forced to seal off an engine room with his own men inside to prevent a deadly gas leak from killing the entire crew, a moment that shows the heavy toll of his command. His authority is such that, while he dislikes being called by military titles, the crew of the Nautilus follows his orders without question, trusting in his wisdom and resolve.