Margaret Cavendish, Duchess of Newcastle-upon-Tyne (1623 – 15 December 1673) was an English aristocrat and a prolific writer. Born Margaret Lucas, she was the youngest sister of prominent royalists Sir John Lucas and Sir Charles Lucas. She became an attendant of Queen Henrietta Maria and travelled with her into exile in France, living for a time at the court of the young King Louis XIV. She became the second wife of William Cavendish, 1st Duke of Newcastle-upon-Tyne in 1645, when she was a marquess.
Cavendish was a poet, philosopher, writer of prose romances, essayist, playwright and, some say, a tireless self-publicist, publishing under her own name at a time when most women writers published anonymously. Her writing addressed a number of topics, including gender, power, manners, scientific method, and animal protection. Her romance, The Blazing World, is one of the earliest examples of science fiction.
Cavendish has been championed and criticized as a unique and groundbreaking woman writer. Samuel Pepys called her "mad, conceited and ridiculous." She rejected the Aristotelianism and mechanical philosophy of the seventeenth century. She criticized and engaged with the members of the Royal Society of London and the philosophers Thomas Hobbes, René Descartes, and Robert Boyle. She has been claimed as an advocate for animals and as an early opponent of animal testing. Cavendish was the only seventeenth century woman to publish numerous books on natural philosophy.