Aqua Man

Atlanna was forced to leave when Atlantean commandos led by King Orvax stormed her home to bring her back to Atlantis. Despite fighting fiercely to protect her family, she was ultimately overpowered and had to flee to ensure their safety. Before leaving, she promised Thomas she would return someday and entrusted Arthur with her trident as a symbol of his potential future as a leader.

Earlier, Atlanna's wound when she washes ashore hints that she was already being hunted by her own people.

Atlanna escaped her execution at the hands of her own Atlantean people. The film reveals she fled to the uncharted seas in exile, where she remained alive until returning to reunite with Thomas at the end of the movie. Her survival is revealed when she appears alive during Arthur's coronation.

Arthur remains hesitant because he is haunted by the belief that his mother was executed for bearing his child, his mixed heritage. This trauma makes him distrust Atlantis and question whether he belongs there, despite Mera's urging and his clear qualifications as the true heir.

Arthur's childhood shows him struggling with being different, as he was bullied for his abilities and heritage.

The Trident of Atlan is a legendary weapon hidden behind a waterfall in Atlantis, originally belonging to the first king of Atlantis. It is the only artifact that can legitimize a claim to the throne, which is why Orm seeks it and why Mera urges Arthur to find it before Orm does. Only a true king can wield its power.

Mera reveals the Trident's existence early in the film as the key to stopping Orm's plans.

Orm, Arthur's half-brother and current king of Atlantis, plots to unite the underwater kingdoms and launch a war against the surface world. He frames it as a defensive measure to protect Atlantis from surface-world pollution and threats, but his true intention is conquest and subjugation of both land and sea.

Orm's hostility toward surface dwellers is established early when he attacks a submarine in Atlantean waters.

Arthur faces Karathen, a colossal sea creature that guards the Trident of Atlan. Using his unique Atlantean ability to communicate with sea creatures, Arthur connects with Karathen and proves his worthiness. This communication ability is what separates him from other challengers and earns him the right to wield the legendary trident.

Arthur's childhood ability to communicate with marine life at the aquarium foreshadows this moment.

Arthur chooses mercy over vengeance when he defeats Orm, now calling himself Ocean Master. Despite Orm's attempt to conquer the surface world and harm his family, Arthur spares his life recognizing their shared history as half-brothers. This act of mercy is what finally earns Arthur acceptance as the legitimate king of Atlantis.

David Kane, who becomes Black Manta, seeks revenge against Arthur because his father Jesse Kane was killed during their confrontation on the submarine. When Arthur refused to save Jesse after he killed innocents, David witnessed his father's death. In the mid-credits scene, David allies with conspiracy theorist Stephen Shin to find and kill Arthur.

The submarine battle establishes the father-son dynamic and David's presence during Jesse's death.

Nereus, king of the Fisherman Kingdom and father of Mera, initially considers allying with Orm. After Orm orchestrates an attack on Atlantis that results in casualties, Nereus is convinced that the surface world is a genuine threat and decides to side with Orm, believing Atlantis needs to unite against common enemies.

Arthur becomes king by retrieving the Trident of Atlan, the only weapon that can legitimize his claim to the throne. After proving himself worthy by communicating with Karathen, he pulls the trident from King Atlan's skeleton. With this power, he defeats Orm in battle, spares his life, and is accepted as the rightful ruler. His mother Atlanna's return also helps solidify his legitimacy.

Mera explains early on that whoever wields the Trident can claim the throne.