Queen Bean is the ruler of the Beanbean Kingdom during the events of Mario & Luigi: Superstar Saga. She is a wise ruler and is able to keep control of her kingdom in the most dire of circumstances, including Bowletta's massive military strike against the peaceful kingdom. She is also the mother of Prince Peasley.
During Cackletta's attempted takeover of the Beanbean Kingdom, the Bean witch force-fed Queen Bean a Belly Blech Worm. The worm caused Queen Bean to grow huge muscles but limited her brain functions to thoughts of destruction. When Mario and Luigi arrive in the throne room, the Queen goes on a rampage, pummeling the plumbers with her massive arms. After a difficult battle, Mario and Luigi eventually overcome the hulking monstrosity. Then Lady Lima, the Queen's aide, appears in the room and explains that the Queen was changed by Cackletta. She tells the Mario brothers that the only known cure for the Queen's condition is a special soda: the Chuckola Reserve. Thus Mario and Luigi vow to find the soda and cure the Queen.
After Mario and Luigi acquire some Chucklehuck Reserve, they return to the castle. Then Mario drinks the soda and spits it into the Queen's mouth. Queen Bean returns to her normal (yet still large) size and is immediately recovered. The Queen then promises to assist the plumbers in whatever way she can in their attempt to stop Cackletta.
Queen Bean has special Beanbean Advisors that serve the same role as Princess Peach's Mushroom Retainers.
It is unknown if there has ever been a King Bean, but, considering that Queen Bean has a son, there was one most likely. It is possible that this mysterious king is dead.