Literary biographer, critic, fiction writer, moralist, and poet, Samuel Johnson was one of the two or three most important figures in eighteenth-century British literary history. His most notable poem, The Vanity of Human Wishes (1749), makes its content clear in its title. His fable Rasselas, first published under the title The Prince of Abissinia (1759), narrates the story of the residents of a fictional Happy Valley, who enjoy gratification of all wants, but nevertheless find themselves discontented because they have nothing to long or hope for and so no outlet to exercise imagination. He is also known for his allegorical moral tale Vision of Theodore (1748). His two essay periodicals, The Rambler (1750-1752) and The Idler (1758-1760), were well received, though not as popular as predecessors such as Joseph Addison's Spectator. Johnson's Dictionary of the English Language (1755), a massive undertaking for a single researcher, remained the standard for a century after its publication. Johnson's own commentary in The Plays of Shakespeare (1765) was later supplemented with the remarks of George Steevens (1773) to become one of the landmarks in the history of Shakespeare criticism. But Johnson's most important contribution to criticism is his Prefaces, Biographical and Critical, to the Works of the English Poets (1779-81), better known as The Lives of the Poets.