Short answers, pulled from the story.
Simonetta Vespucci was an Italian noblewoman from Genoa, born around 1453, who married Marco Vespucci of Florence and was widely regarded as the greatest beauty of her age in Italy. She became famous partly through her connection to the Medici family and through the jousting tournament of 1475, where Giuliano de Medici rode beneath a Botticelli banner depicting her as Pallas Athene and named her Queen of Beauty.
Simonetta Vespucci was related to Amerigo Vespucci by marriage, not by blood. Her husband Marco Vespucci was a distant cousin of the explorer and cartographer Amerigo Vespucci, making Simonetta his cousin-in-law.
Simonetta Vespucci died on the night of the 26th-the 27th of April 1476 at the age of twenty-two. Tuberculosis was the traditional explanation. In 2019, a team of medical historians proposed that she may have died from a pituitary adenoma secreting prolactin and growth hormone, with the increase in tumour volume as the cause of death.
The claim that Simonetta Vespucci was the model for the Venus in The Birth of Venus is widely disputed. Ernst Gombrich called it a "romantic myth" and historian Felipe Fernandez-Armesto called it "romantic nonsense." Botticelli completed the painting around 1486, ten years after Simonetta's death. The one portrait Botticelli is known to have made of her was the banner painted for the 1475 joust, which is now lost.
Botticelli's parish church from baptism was the Church of Ognissanti in Florence, which was also the Vespucci family's parish church. He was buried there in 1510, thirty-four years after Simonetta's death, alongside his own family. His principal Medici patron, Lorenzo di Pierfrancesco de Medici, married Simonetta's niece Semiramide in 1482.
The Victorian critic John Ruskin has been identified as a key figure in spreading the attribution linking Simonetta Vespucci to multiple Botticelli paintings. Some art historians have taken issue with these attributions and trace the romantic tradition to Ruskin's influence rather than to documented Renaissance sources.