In the original film, King Frederic was said to be a beloved ruler alongside Queen Arianna, and was also shown to be deathly devoted to his family. When Rapunzel was kidnapped by the wicked Mother Gothel, he was devastated, and remained as such for the following years to the point where the anniversary of Rapunzel's disappearance drove him to tears even eighteen years later. The moment his daughter was returned, however, King Frederic embraced his restored family and, as seen in Tangled: Before Ever After, vowed to never let anything happen to them again, especially Rapunzel.
Gothel's actions drove Frederic to an understandably paranoid state of mind. Likely suffering from Post Traumatic Stress Disorder, Frederic cracked down on his security forces throughout the kingdom. Despite his overwhelming joy toward Rapunzel's return, he was admittedly unable to separate "the father from the king", therefore creating laws, rules and restrictions that limited Rapunzel's freedom in hopes of preventing another catastrophe similar to his daughter's kidnapping at the hands of Gothel. This creates tension between Frederic and Rapunzel, but despite his firm attitude on the matter, Frederic tries his best to make Rapunzel feel happy and content with her new life. However, his constant need to keep secrets and lack of trust in his daughter only further pushes the two of them apart. Because of this, Frederic had been compared to Gothel by both Rapunzel and Eugene.
Despite his firmness, Frederic is a kind and noble ruler at his core. He cares a great deal for Corona and its people and shows a great deal of compassion and respect to his subjects. Frederic does not take kindness and loyalty for granted; as mentioned in "Queen for a Day", Frederic was able to recognize the goodness in former rogues such as Flynn Rider and the Pub Thugs, and in turn provided them with opportunities to change their lives for the better, despite the borderline negative reception such an act received from his staff and subjects. While his actions can be dubious, Frederic is well-intentioned. He was nevertheless able to recognize the selfish nature of his decisions, and how they were causing a great deal of harm for both his family and his people. As such, he forced himself to confront his inner demons and change for the better. The result was a reformed relationship between his family and subjects, one built on trust.
Father to Rapunzel, and husband to Queen Arianna, Frederic is the ruler of Corona. He is first seen by his wife's sickbed while she is heavily pregnant with their daughter and lighting the lantern with Arianna later on after Rapunzel's birth. Every year on Rapunzel's birthday, Frederic and Arianna release a lantern for their daughter. He is seen releasing the lantern again, the night Rapunzel arrives with Flynn Rider to watch the lanterns float. He weeps silently while preparing for the launch of the first lantern, and is comforted by Arianna. These scenes show that he and Arianna have a close and loving relationship and that they still grieve for their lost daughter. Frederic returns to the scene towards the end when Rapunzel returns to reunite with him and Arianna. He is then seen again smiling and hugging Rapunzel and Arianna. Although Frederic, like Arianna and many other minor and supporting characters, does not speak, he has vivid and lively facial emotions and body languages that loudly and clearly express his thoughts and ideas.
In the short film, Rapunzel and Eugene's wedding day has finally arrived. Frederic is obviously present the day of and walks Rapunzel down the aisle. After escorting his daughter to the altar, he sat down to join his wife in watching the ceremony as the priest officiated the wedding vows. Upon asking Maximus and Pascal for the rings, everyone, Frederic included, were shocked to see the two animals covered in tar, and stared awkwardly as they held up the rings to the happy couple. After exchanging rings, the priest officially declared Rapunzel and Eugene married. Frederic hugged his wife while the rest of the audience cheered.
Taking place six months after Tangled and before the events of Tangled: Ever After, Frederic is overjoyed to have Rapunzel in the sanctity of the castle once more. As her coronation draws near, Frederic reminds his daughter that the duties of a princess are important for both the kingdom and their family, despite how time-consuming they can be. Rapunzel asks for some downtime, but Frederic believes it would be unnecessary, and that Rapunzel simply needs some time to settle into the lifestyle. Additionally, in preparation for the coronation, Frederic has upped the security in Corona, including a wall blocking the kingdom from the rest of the world. This wall and her father's overbearing nature as a whole has Rapunzel feeling trapped and confined. With the help of her handmaiden Cassandra, Rapunzel crosses Corona's wall and journeys into the world surrounding it overnight. During the outing, she finds mysterious rocks that cause her magic golden hair to return.
Back at the castle, Frederic and Arianna talk over the former's paranoia, and this encourages the king to at least rethink his methods of protecting Rapunzel. At the coronation, however, Frederic nearly becomes victim to a revenge plot headed by a pirate named Lady Caine. Rapunzel protects her father and the other royal guests by using her hair as a weapon and fighting the Pirates off. After Caine's arrest, Rapunzel explains the truth to her father about the hair. In response, Frederic tries to explain the reasoning for his overprotective behavior, explaining that, after his daughter's kidnapping eighteen years prior, "a part of him died", and since then, he has been unable to shake off the worry that a new danger is always close by. As such, he feels the return of the magic hair may attract a threat similar to Gothel, and thusly enacts a new law that prevents Rapunzel from leaving the confines of the kingdom without his consent. He also orders his daughter to never speak of the magic of any kind from that moment forward, all of which drives her to tears. Frederic, meanwhile, can only hang his head in guilt and disappointment at this, as he secretly feels he is doing a terrible thing to his daughter.
Frederic appears in the series taking place immediately after Tangled: Before Ever After, where he continues to govern the kingdom while also finding time to grow and develop as a person, specifically in his relationship with Rapunzel. In "What the Hair?!", a week after Frederic and Rapunzel's falling out, it is revealed that neither of the two have spoken to one another about the matter, which distracts Frederic a great deal from his normal activities. Arianna urges him to talk with his daughter, but he refuses. In "The Wrath of Ruthless Ruth", Frederic finds Rapunzel's journal, opened, and fondly looks through his daughter's illustrations. He soon finds, however, that the illustrations are recaps of his daughter's recent, high-risk adventures within the kingdom. Fearful that Rapunzel will get into harm's way despite obeying his law of staying within Corona's walls, Frederic orders the Captain of the Guards to double down on Rapunzel's security. Rapunzel quickly takes notice of this and becomes motivated to confront her father on his shielding. Upon arriving within her father's quarters, Rapunzel finds the king in a distraught state. He hurriedly embraces his daughter and professes his love for her. Rapunzel comes to realize that her father's actions are out of genuine love, and in response, chooses to keep her feelings undisclosed by simply returning his sentiments.
In the episode, "The Quest for Varian" Frederic is very upset and angry when Rapunzel brings up the black rocks again, after having a nightmare. When Rapunzel continued to demand answers, he took her to his planning room. He showed her black flags that represented the mysterious rocks and claimed that he had been having them carefully removed to prevent outright panic. As Rapunzel leaves, the King's expression changes to worry and sorrow.
At the end of the episode it is revealed that King Frederic deliberately lied to his daughter. Not only had he not gotten rid of the rocks, he also sent the guards in disguise, to capture Rapunzel before she found a secret scroll that contained information about the connection between Rapunzel's hair and the strange rocks.
In the following episode, “The Alchemist Returns”, King Frederic is confronted by Rapunzel by the fact not only did he lie to her, he sent his guards after her to prevent her from obtaining a secret scroll about a connection between the magical golden flower and the black rocks. Frederic defends himself saying he was doing what was best for Corona, and more importantly, Rapunzel. No matter how much Rapunzel demands the truth, he continues to tell her she is not ready for the real world.
Rapunzel then storms off, but not before stating that someone else once lied to her and said she wasn't ready for the real world. Frederic realizes that Rapunzel is comparing him to Mother Gothel and is visibly hurt by the comparison, but still won't tell Rapunzel the truth. Later in the episode it is revealed that another secret that Frederic hid was that the magical flower still existed and that it was in the royal vault.
In the first season finale, "Secret of the Sun Drop", Frederic went as far as imprisoning Rapunzel in her bedroom tower, including bars on her window to keep her safe, after one of Varian's automatons attacked. His wife disagreed with his actions, but could not change his mind. Later after his wife was kidnapped he broke down in his bedroom, stricken with grief at losing another member of his family to kidnapping. When Rapunzel comforts him and tells him this is not his fault, Frederic replies that it "is" his fault.
He revealed his final secret about what happened on the night Rapunzel was born. He had been warned by Quirin that by taking the Sun-Drop Flower would unleash a darkness upon the kingdom with deadly consequences. He did not heed the warning and used the flower. He revealed he knew about the black rocks the whole time and knew they were connected to Rapunzel. Unable to handle losing her again, he kept a constant vigil on her. He also stated that he tried to remove the rocks, but when he could not he chose to ignore them and hoped everyone else would. These actions were not of a king, but a father.
A short time later, Frederic joined Rapunzel as they went on a rescue mission to save the Queen, only to walk into Varian's trap. He demanded that Varian releases them which was promptly ignored. He stood by helplessly while the alchemist threatens to trap Arianna in amber if Rapunzel did not help him free his father with her hair. When it did not work, the King got his family to safety only to see his daughter end up trapped in the black rocks. He then witnessed Rapunzel use the rocks to stop Varian and saw them become a pathway leading out of the kingdom. After promising to help both Varian and his father, Frederic admitted that he finally saw that Rapunzel was a strong individual who could take care of herself. He gave her permission to follow the rocks to embrace her destiny while stating when she was ready to come back, the lanterns would light the way back.
Frederic and Arianna make a brief appearance at the end of the episode "The Tower", where they are seen reuniting with Rapunzel after years of separation.
Interestingly, by the end of Tangled: Before Ever After, Frederic's paranoia has morphed him into an overbearing parental figure eerily similar to Mother Gothel, as he forbid Rapunzel the freedom she craves. The difference is Frederic's actions are out of genuine love, while Gothel's were out of selfishness for the hair's power.
In "In Like Flynn", Frederic mentions that he's had extensive military training.
According to Rapunzel in "In Like Flynn", Frederic likes to tell jokes, though they're not very good.
In the original fairy tale of which Tangled is based on, Rapunzel's parents (who weren't royalty) lived next door to the witch and often admired how large her garden was. While Rapunzel's mother was pregnant, Rapunzel's father snuck into the garden, stole some of the vegetables growing and got caught. The witch let him go in exchange for the baby he and his wife were having. They're never seen after that.
The King in Once Upon a Time
Rapunzel's journal sketch of King Frederic, following their emotional falling out