Margaret King (1773–1835), also known as Lady Mount Cashell and Mrs Mason, was an Irish hostess, writer, traveller, and medical adviser. Despite her wealthy aristocratic background, she had republican sympathies, shaped in part by having been a favoured pupil of Mary Wollstonecraft. In Italy in later life, she reciprocated her governess's care by offering maternal aid and advice to Wollstonecraft's daughter Mary Shelley (author of Frankenstein) and her travelling companions, husband Percy Bysshe Shelley and stepsister Claire Clairmont.