Immanuel Kant
Kant developed his moral philosophy in three works: "Groundwork of the Metaphysic of Morals" (1785), "Critique of Practical Reason" (1788), and "Metaphysics of Morals" (1797).
John Keats
When Keats died at 25, he had been writing poetry seriously for only about six years, from 1814 until the summer of 1820; and publishing for only four. In his lifetime, sales of Keats' three volumes of poetry probably amounted to only 200 copies. His first poem, the sonnet "O Solitude" appeared in "the Examiner" in May 1816, while his collection "Lamia, Isabella, The Eve of St. Agnes and other poems" was published in July 1820 before his last visit to Rome. The compression of his poetic apprenticeship and maturity into so short a time is just one remarkable aspect of Keats' work.