Belle Gunness, also known as Hell's Belle, was a Norwegian-American serial killer active in Illinois and Indiana between 1884 and 1908. She is believed to have murdered at least fourteen people, with some sources speculating her involvement in up to forty murders. Gunness, born Brynhild Paulsdatter Størseth in Norway, immigrated to the United States in 1881. She married Mads Ditlev Anton Sørensen in 1884 and later Peter Gunness in 1902. Both husbands and several others associated with Gunness met mysterious deaths, often followed by substantial insurance payouts to her. Her criminal activities were exposed in 1908 when the Gunness farmhouse in La Porte, Indiana burned down, revealing multiple bodies, including those of her children. The discovery led to the investigation of at least eleven additional partial remains on her property. The actual fate of Belle Gunness remains unconfirmed, and she is considered one of the most prolific female serial killers in history.

Belle da Costa Greene (November 26, 1879 – May 10, 1950) was an American librarian known for managing and developing J. P. Morgan's personal library. Despite being born to black parents, Greene spent her professional career passing for white. Born as Belle Marion Greener, she and her family changed their surname to Greene and claimed a Portuguese background, distancing themselves from their African-American heritage. Greene's education was funded by philanthropist Grace Hoadley Dodge, and she later attended the Amherst College's Summer School of Library Economy. She began her career at Princeton University Library, where she met Junius Spencer Morgan II, leading to her role as J. P. Morgan's librarian in 1905. Greene's expertise in rare books and illuminated manuscripts made her a trusted representative of Morgan abroad. She played a pivotal role in acquiring and selling rare manuscripts, books, and art for Morgan, aiming to make his library "pre-eminent." Greene's influence extended to supporting artists like Edward Curtis in his project to preserve Native American life. Her legacy as a librarian and art advisor remains significant in the history of library science and art preservation.

Belle Starr, originally named Myra Maybelle Shirley, was an infamous American outlaw who gained national notoriety after her violent death. Born on February 5, 1848, in Carthage, Missouri, she was associated with the James–Younger Gang and other outlaws. Known for her strong sense of style, Belle was a crack shot and often rode sidesaddle while dressed in a black velvet riding habit and an ostrich feather-plumed hat, carrying two pistols and cartridge belts. After marrying a Cherokee man named Sam Starr, she settled with the Starr family in the Indian Territory, where she engaged in illegal enterprises, including organizing, planning, and fencing for rustlers, horse thieves, and bootleggers. Belle's criminal activities proved lucrative, enabling her to employ bribery to free her colleagues from the law whenever they were caught. Despite being convicted of horse theft in 1883, Belle's story was popularized by Richard Kyle Fox, and she later became a popular character in television and films. Her life and mysterious death continue to captivate the public, as the case remains officially unsolved.

Maria Isabella Boyd, better known as Belle Boyd, was a prominent Confederate spy during the American Civil War. Born on May 9, 1844, in Martinsburg, Virginia, Boyd's espionage career began when she shot a Union soldier who insulted her mother. She charmed Union officers, gaining valuable information that she passed on to Confederate officers. Boyd's most famous feat was eavesdropping on a meeting of General James Shields and his staff, riding through Union lines to report their plans to the Confederates. Despite being arrested multiple times, Boyd managed to evade incarceration. Following the war, she married and became an actress in England before returning to the United States. Boyd then toured the country giving dramatic lectures about her life as a Civil War spy. She published a fictionalized account of her war experiences in "Belle Boyd in Camp and Prison" before passing away on June 11, 1900, at the age of 56. Her legacy as the "Cleopatra of the Secession" lives on in popular culture.

Belle Moskowitz (October 5, 1877 – January 2, 1933) was a significant figure in the early 20th century as a Progressive reformer and political influencer. The New York Times described her as the most powerful woman in U.S. politics in her obituary. Born Belle Lindner in 1877 in Harlem, New York City, to immigrant parents from East Prussia, Belle was exposed to charitable activities at a young age through the temple's female Sisterhood. She attended Horace Mann School and later studied at Teachers College, Columbia University. Initially pursuing a career in acting, she later transitioned to politics. Belle's early career involved social work, writing, and advocacy for women and labor reforms. She played a crucial role in improving the moral surroundings of young girls by regulating dance hall conditions. Belle also established The Lakeview Home for Girls and aligned with the platform of Theodore Roosevelt's Progressive Party during the 1912 presidential election. She mediated labor disputes and provided counseling for factory planning and employment management. Belle Moskowitz's contributions to social reform and politics left a lasting impact on U.S. history.