Henry Mills is Emma Swan and Neal Cassidy's son, whom she gave up for adoption after giving birth following her release from a federal correctional facility in Phoenix, Arizona in 2001. He is also Snow White, Prince Charming and Rumplestiltskin's grandson, and the great-grandson of the latter's father's alias Peter Pan. He is adopted by Regina Mills (the Evil Queen), after Mr. Gold (Rumplestiltskin) procures him, naming him after her late father. At first Regina had a little difficulty raising Henry but grew to love him, thus preventing Henry from being taken by the Darling Brothers, who wanted to take Henry to Neverland on orders from Peter Pan.
As Henry gets older, his relationship with Regina became strained, and she sends him to regular therapy sessions. When he is ten, he receives his cherished book of fairy tales from his teacher Mary Margaret Blanchard (Snow White), discovering that the residents of Storybrooke are characters from it after noticing he is the only one in town who ages. Henry finds his biological mother Emma Swan in Boston and brings her to Storybrooke. He eventually convinces her of the truth by consuming a sleeping curse intended for her by Regina, nearly resulting in him dying. However, he is awoken with true love's kiss by Emma, which also breaks the curse. Emma and Mary Margaret are then dragged into a portal, leaving David (Prince Charming) to look after him. Following the death of Regina's mother Cora, and her vowing to avenge Mary Margaret, Henry seeks to remove magic from Storybrooke. When Emma and Regina stop the trigger enacted by Greg Mendell and Tamara from destroying the town, he is kidnapped by the pair and taken to Neverland, where it is revealed that Peter Pan (Henry's great-grandfather) wants possession of him as he owns "the heart of the truest believer".
Pan eventually persuades Henry to give him his heart, telling him it will save magic. Regina reclaims the heart and resurrects Henry. However, Pan inhabits Henry's body in Storybrooke, enacting Regina's original curse once more. Mr. Gold returns Henry to his body, and Emma and Henry escape to New York City whilst the remaining residents return to the Enchanted Forest. A year later, Hook restores Emma's memories, leading her to return to Storybrooke with Henry to save their family from another curse. Henry is confused about Emma's decision to relocate, until his past memories are restored with his book. Once his memories are restored, Regina gives him true love's kiss breaking the curse. Henry then moves back to Storybrooke where he splits his time living with Regina and the Charmings. Henry later helps Regina to search for his storybook's author, Isaac. Upon discovering the writer's manipulative actions, Henry being the only one born in the Land Without Magic is left behind in Storybrooke and goes to find Isaac and enters his new storybook "Heroes and Viilains" to fix reality and after saving Emma who remembers everything they both try to help Regina get her happy ending to fix reality but fail. Then Henry takes the pen and becomes the next author and using Regina's blood to write a new ending to fix reality. With Henry being the new author and he breaks the pen deeming it too powerful for anyone to use. Henry then watches Emma sacrificing herself to save Regina and Storybrooke by becoming the new Dark One.
With his family and a few of the other residents, Henry transports to the Enchanted Forest to find Emma and to take her to Camelot in order to find Merlin and remove her darkness. However, six weeks later, they return to Storybrooke with missing memories as to how they all failed to get the darkness out of Emma except Henry. Revealed in a flashback, Henry has fallen in love with a girl named Violet; due to needing a tear from the pain of losing a first love to help free Merlin, Emma tearfully manipulates Violet into breaking Henry's heart. Due to Emma's curse, Henry gets another chance with Violet, as neither remembered each other from before; they end up sharing a kiss.
After Emma restored his memory, Henry helps Emma rescue Hook after he is sent to the Underworld for sacrificing himself to save everyone. When he arrived with his family, he comes up with a new plan called "Operation Firebird," this after learning that they have a chance to save the souls and help them move forward. However, when he comes across Cruella De Vil, he is offered a chance to help her return to the living as he is the Author, this after telling him that despite having broken the quill in two he still has the ability to use the quill and magically write her a new life while he was in the underworld and at the same time restore Emma's soul as forgiveness, but this would put Henry in a situation that would force him to break his vow not to tamper with his family history. He then learns that he has the ability to bring others back from the dead when he came across the Apprentice, whose soul can't move on until Henry makes the right choice, which is to record the events in the book. Henry plans to re-write Hades' story that was missing in the Underworld version of the "Once Upon a Time" book. He also starts experiencing visions that allows him to illustrate stories but can not explain why they're coming to him. Before he returned to Storybrooke, he finished the unfinished businesses in the book, only to have Cruella hide it in Hades' lair.
Upon returning to Storybrooke, Henry began to experience a roguish streak as he believed magic is destroying his family in the wake of Robin Hood's death. This prompts him and Violet to obtain the Olympian Crystal and flee to New York City where magic can be destroyed. However, his actions also resulted in leaving Snow, David, Zelena, and Hook in the Land of Untold Stories when he used a holy grail to destroy it. Having regret what he did, Henry turned to a fountain and made a wish that he would reunite his family, and with the help of Emma, Regina, Violet, and Gold, along the New Yorkers who see him make this plea, the fountain succeeds in bringing Snow, David, Zelena, and Hook to New York and with that restored magic. Upon returning to Storybrooke, Henry learned that Violet, although born in Camelot, was actually from Connecticut, due to her father having slipped into an unknown portal. The then shared a kiss, implying that are now a couple, as he has found his happy ending.
After Henry and Regina meet with Mr. Hyde who has arrived in Storybrooke with his friends from the Land of Untold Stories, he and his family devised a plan to imprison Hyde which succeeds and later welcomes the new residents with food and shelter at Granny's. The next day Henry and Regina arrive at Granny's with a new plan called "Operation Cobra Part 2", and as Henry begins to write the names of the people of the Land of Untold Stories, a mysterious man leaves a note beside him for Snow and David revealing his name as Edmond Dantès also known as the "Count of Monte Cristo". Regina then reveals she hired him to kill them back in the Enchanted Forest and after he refuses to back down from trying to kill them Regina and Henry discover a girl named Charlotte who was Snow and David's handmaiden and who also resembled Edmond's dead fiance. The Evil Queen then reveals herself to both Henry and Regina and reveals that she has been controlling Edmond the whole time. As soon as he is about to kill Snow and David, Regina steps in to save them and after Henry's phone is frozen with magic Regina is forced to kill Edmond. Henry then realizes that this new operation will be harder as Part 1 was about giving people back their happy endings and now in Part 2 these people ran away from their stories,
Afterwards, Henry has written down all the names of the new residents and he, Emma, and Hook find out Ashley's (Cinderella) step-sister Clorinda is now in town and they believe she wants to hurt but really wants to help her. After Emma's magic fails because of her hand trembling, the Evil Queen shows up and after Henry tells her to leave his mom alone she points out that she is his mother too and poofs the three of them onto a road somewhere in town to stop them from helping Ashley but they save her and her step-sister as well. After Henry and Violet start school together with Snow returning as a teacher.
When Henry and his family learn about Emma's secret they are shocked and hurt by it and for Emma not telling them and Henry then starts to blame himself for bringing her to Storybrooke for her to become the savior but she tells him that what he did gave her a better life despite that she might die. After they find Aladdin who reveals he use the "Shears of Destiny" to cut off his destiny as a savior, Emma wants to throw them away because she being the savior is what makes her special and she will not use them but Hook secretly keeps them and this causes the Evil Queen to try and cause a shift between Hook's and Henry's relationship but it fails when they both agree all they wanted to do is to protect and save Emma.
When the Evil Queen teams up with Mr. Gold and threatens the town with water from the River of Lost Souls, Henry along with everyone is forced to watch the Queen rip out Snow White and David's shared heart and put a twisted sleeping curse on it. After revealing that when one of them is awake and the other will be asleep, Henry agrees to lure the Evil Queen out for Emma and Regina to try to trap her and as a distraction from being nervous about taking Violet to the school dance believing she doesn't like him anymore but really is having a hard time adjusting to school and after the Evil Queen fails to darken Henry's heart by smashing the mirror instead of the Dragon's heart to save Emma and Regina.
Jared, who had previously starred in Mad Men as the third Bobby Draper from 2009 to 2011, was cast in Once Upon a Time as Henry Mills, the "biological son of Emma Swan (Jennifer Morrison's character) and Neal/Baelfire. He is the only resident of Storybrooke who is not under the spell of the Evil Queen (Lana Parrilla)." Series creators Adam Horowitz and Eddy Kitsis stated of the role, "One of our emotional centers was an 11-year-old boy who had to be precocious and vulnerable at the same time." Kitsis believed that Gilmore "naturally brought [these characteristics] out... We just knew he had to be our Henry!" Gilmore commented, "I relate to Henry because I'm 11 and also have a very good imagination. I enjoy making up and playing games in worlds with alternate realities myself."