King Riku is the current King of Dressrosa. He gained love and loyalty of everyone in his country until the day when the Donquixote pirate group came to Dressrosa and plotted to take the throne. Kink Riku fell victim for their plot and ended up dethroned from his position as the King of Dressrosa. He also lost the trust and love of many of his own people. This continued for 10 years, until the day the Strawhats came to Dressrosa. The entire plot that happened 10 years back has been exposed to the public and Monkey D. Luffy defeated Doflamingo who was the mastermind behind the whole event. Eventually, King Riku has been recrowned as the King of Dressrosa after the fall of the pirate group who took over this country for 10 years.
Matriarch was the queen of Dressrosa. She was the wife of KingĀ Riku Doldo III and the mother of both Scarlett and Viola. Not much is known about this character and It's unknown when and how she died.
Scarlett is the eldest daughter of King Riku Doldo III and Queen Riku Matriarch. She got married to Kyros who originally was assigned to protect her and to be her guard. She has one daughter only, her name is Rebecca. She lived in a small house with her little family away from the castle until she was killed by the Donquixote family.
Kyros is the legendary gladiator of Dressrosa who is known for having the longest winning streak of 1000 match at Corrida Colosseum. Everyone forgot about him once he has been turned into a toy by Sugar's power, however, he has a status of him at the Colosseum that all the gladiators considered him to be a legendary gladiator without even remembering him. Kyros got married to Scarlett the daughter of Riku Doldo III and he is the father of Rebecca.
Rebecca is Currently she is the princess of Dressrosa. She is the only daughter of Scarlett and Kyros and she is the only granddaughter of King Riku Doldo III. She was hated by the citizens of Dressrosa for being of the dethroned royal family. As a kid she was trained by the toy solider without knowing that he is actually her father but he was turned into a toy and she lost all memories regarding him. By the age of 16 she became a gladiator and she was fighting at the Corrida Colosseum.
Viola is the second daughter of King Riku Doldo III and Queen Riku Matriarch. She possess the power of Giro Giro devil fruit. After the dethronement of her father, she was forced to join the Donquixote family against her own free will and that was because of her Devil fruit that the Donquixote family wanted to utilize for their benefits. She served under Donquixote Family for years before she decided to that it's the right time to betray them and she sided with the Strawhats.