Captain Nemo is a minor character on Once Upon a Time.
After the Curse
Nemo pays a price for getting in the way of Liam's revenge. ("Dark Waters")
While Captain Nemo was out at sea, his family was brutally murdered by a group of men he spent decades hunting down. Eventually, when he was finally able to find them, he slaughtered them all, but he soon found all he was left with was an empty heart and a blood-stained harpoon. That same harpoon is enchanted to help him find wayward souls whose hearts are also full of vengeance, and help to rehabilitate them so that they don't end up like him. One of the boys Nemo mentors while captaining his submarine, the Nautilus, is Liam Jones II, whom he spared from the magic of the Dark Curse. Liam, whose father was murdered when he was a boy, comes to view Nemo like a second dad, and is eventually promoted to first mate. Nemo soon uses his harpoon to track down Captain Hook, whose pirate ship he stows away on so that he is able to kidnap him. He tells Hook his story and how he should give up looking for vengeance, then requesting that the pirate help him on his quest to find a key to the mysterious island - otherwise known as the Land of Untold Stories. During the quest, Nemo rescues Hook from a kraken, assuring him that he's part of his family now, but Hook seems less than eager to join upon realizing that Nemo's first mate is in fact his half-brother Liam... whose father he killed. Liam overhears this and tries to kill Hook, only for Nemo to step in the way and receive his first mate's knife to the gut instead. While Hook escapes, Liam manages to save his mentor by using the key to pause his story over in the Land of Untold Stories. ("Dark Waters")
After the Third Curse
Hook reunites Nemo and Liam, in Storybrooke. ("Dark Waters")
Nemo and Liam are among those to be plucked by Mr. Hyde from the Land of Untold Stories and brought to the town of Storybrooke so that their stories can finally play put. For Nemo, this means finally succumbing to his stab wound and bleeding out in the woods, with Liam believing him to be dead. However, he is discovered by David, the sheriff, and rushed to the local hospital. There, Dr. Whale is successful in saving his life, and he is eventually able to reunite with Liam after he and his brother Hook unexpectedly manage to put their past behind them and make amends. ("Dark Waters")
Hook asks to join Nemo's crew. ("Page 23")
While contemplating things over at the docks, Hook is approached by Captain Nemo, who announces that he and his crew are to be setting sail aboard the Nautilus and leaving Storybrooke. Nemo is happy to see that Hook has taken his advice and set aside revenge in order to find a family, but Hook shows pangs of guilt and admits that he did something to destroy the very family that he's trying to be a part of. Nemo warns him that guilt can be just as corrosive to the soul as revenge, and so gives him two new pieces of advice: either he can tell his new fiancée and her family the truth of what he did... or he can keep it a secret, and learn to forgive himself. Unfortunately, Hook tries taking a third option by burning his memories, only for his love to catch him and call off their engagement. She gives him back his ring, and he goes to Captain Nemo and asks to join him aboard the Nautilus when it sets sail. However, Snow later approaches Hook with the news that the Evil Queen redeemed and got her happy ending, which imbues him with the hope that maybe he can too. He goes to Nemo again, this time on the Nautilus, to tell him that he has to stay and make things right with Emma... but then the submarine submerges, thanks to Gideon tampering with things, for the hooded villain can't have Hook in Storybrooke for what he has planned. ("Page 23")
A pair of captains bid each other goodbye. ("A Wondrous Place")
Thanks to Gideon, the Nautilus finds itself portaling into another realm - the Enchanted Forest. It is Liam Jones II who breaks the news to his brother that they cannot travel back, because to do so would require kraken's blood to fuel the vessel, which they don't have. As such, Hook decides to go hunting, but all he finds in the way of a kraken is Aladdin and Jasmine trying to fend one off. The battle causes irreparable harm to the Nautilus, which soon begins to sink, and so Jasmine uses one of her genie wishes to wish everyone aboard over to Hangman's Island where another villain, Jafar, needs to be faced. Nemo is disappointed not to have gone down with the Nautilus, needing to find it again, and Liam heads off with him. He and his brother share a hug goodbye, acknowledging that they never get long together, while the two captains shake hands and show a mutual respect for one another as they part ways on the beach. ("A Wondrous Place")
Gallery of photographic stills released to promote the character.