The Riku Family is a royal bloodline which ruled the Dressrosa Kingdom from the formation of the World Government, until ten years before the current timeline. It was one of the new royal families after nineteen of the twenty kings that founded the World Government left their kingdoms with their families to live in Mariejois.
Eight hundred years ago, the Riku Family became the new rulers of Dressrosa Kingdom after the Donquixote Family left the country to live in Mariejois. After learning of the era of slavery that the dwarves had suffered at the hands of the Donquixote Family, the first King Riku made a sincere apology. As atonement for the sins of his predecessors, he allowed them to take anything they needed from the humans as they pleased without having to work for it. King Riku told his citizens that the disappearances were the work of "fairies", beginning a legend that would persist through the centuries. Over the years that followed, the reign of the Riku Family was characterized by their generosity, as they focused their efforts on assisting their neighboring countries whenever possible, despite their own lack of wealth.
During the third Riku Dold's rule, he met with Kyros. At first hostile, Kyros eventually became the captain of Riku's army, and the protector of the two princesses: Scarlett and Viola. Kyros and Scarlett eventually fell in love, but due to the public opinion on Kyros' criminal records, the two cannot marry officially, much to Riku's distraught. To be together, Scarlett faked her death and eloped with Kyros, living on the outskirts of the country with their daughter, while forfeiting her right to the throne to Viola.
Ten years ago, a member of the Donquixote Family, Donquixote Doflamingo, came back to his clan's original kingdom to oust the Riku royalty, and regain the king status. Doflamingo tricked Riku Dold III, the current king of Dressrosa, into gathering 10 billion ransom, as that was the only way he would let him keep the island's throne. When Riku started gathering the money, Doflamingo controlled him and his soldiers with his Devil Fruitability and made him attack his own people. Riku, looking like a tyrant who went mad with greed, had to give up the throne due to that incident and was forced into hiding. That incident caused Riku Dold III to lose all the trust from the people of Dressrosa and they soon started to despise the whole Riku family. Doflamingo was intrigued by the king's daughter's Devil Fruit ability and asked her to join his crew, which she accepted in exchange of securing her father's survival. Scarlett was killed by the Donquixote Family soon afterwards and Kyros (now turned into a toy known as Thunder Soldier) took in Rebecca and raised her.
At some point in the past, Rebecca was captured by the Donquixote Family and she was forced to fight in the Corrida Colosseum as a gladiator. Despite her strength and the fact that she survived many battles in the Colosseum, she still received a lot of hatred due to her heritage. Rebecca competed for the Mera Mera no Mi as part of the D Block. She was the winner of D Block after surviving Hakuba's assault, and participated in the final round.
Riku Dold III, who was presumed dead, also fought for Ace's fruit under the Alias "Ricky" in Block B. After he lost the fight, he was thrown into an underground dungeon along with the other defeated fighters. There, his true identity was revealed and he received his old subordinates' and allies' praises. Unfortunately, they were all turned into toys soon after, and Riku was taken hostage in Doflamingo's castle.
After Sugar's fainting and her curse lifted, the citizens of Dressrosa finally see Doflamingo for the tyrant he really was. He was then forced to use his "Birdcage" technique to regain control over the country. The citizens, now forced to attack each other, finally realize what truly happened to King Riku all those years ago and felt utter remorse for believing Doflamingo's trick and how they all betrayed the Riku family.
However, this did not stop them from trying to capture Riku and his family to bring to Doflamingo in order to stop the chaos. But when they actually succeeded, they give up the plan, knowing that it was another lie set up by Doflamingo, as he will not let anyone survive, and beg Riku to stop him.
When Doflamingo was defeated by Monkey D. Luffy, the citizens begged Riku to take back his place on the throne to which refused stating while he relieved that everything Doflamingo did was revealed he had no intention of becoming King. The citizens did not take this answer and pleaded profusely for him to lead them once more as he is there one and only real king. With some more convincing from an old friend, Riku was forced to think it over but this was subsided when marine admiral Issho kneeled down and apologize to the king for allowing Doflamingo to take power and cause chaos on Dressrosa.
Three days later, Riku Dold III was reinstated as the King of Dressrosa with his granddaughter Rebecca becoming the crowned princess as riku intended for her to rule the kingdom one day.