Though he could hardly have expected it during his lifetime, as his work was roundly condemned by conservative commentators of the day, Keats had already become one of the most revered English poets of the Romantic period within a few decades of his death. At the time of his death, he had only been writing poetry for about six years, and had only published three volumes of poetry. In his work, however, he had taken on the challenge of using a wide variety of poetic forms, from the Miltonic epic, to the sonnet, to Spenserian romance, infusing them all with his signature striking sensitivity, verbal adeptness, and impeccable sense of lyricism. Some of his contemporaries, notably his editor and friend Leigh Hunt, and famed poet Percy Bysshe Shelley, championed his work, but they were in the minority. Influenced by Hunt's Examiner, which expressed disdain for Romantic poetry, Keats sometimes declared himself part of a "new school" of poetry; this may have alienated contemporaries.
His posthumous reputation grew steadily, however. The Cambridge Apostles, a secret society of undergraduates which included Alfred Tennyson, a later Poet Laureate, was supportive of his work. His first biography was published in 1848, situating him in the English poetic canon. The Pre-Raphaelite Brotherhood of painters, an English group of moderately well-known artist, also used his poems as inspiration for their work. By the end of the century, his work was decided to include some of the best examples of English poetry. He is widely considered to share the ranks of the major British Romantic poets, Williams Wordsworth, Samuel Taylor Coleridge, William Blake, Lord Byron, and Percy Bysshe Shelley. Commentary by his friend Shelley, who declared that Keats was too finely-tuned and sensitive to survive in a world of unduly harsh criticism, has always colored public perception of Keats and reception to his poetry.
His letters, which were first published in 1848 and 1878, were initially thought of as distractions from his poetry. In the twentieth century, however, they became much more highly regarded. T.S. Eliot wrote, "There is hardly one statement of Keats' about poetry which...will not be found to be true, and what is more, true for greater and more mature poetry than anything Keats ever wrote." He used letter-writing as a way of synthesizing his thoughts and philosophy, especially in the abundant letters he wrote to his brother George and sister-in-law Georgina, who had moved to the United States. Some of his most noted philosophical concepts - the chameleon poet, negative capability, and the Mansion of Many Apartments - took form in his letters. His letters also appear to have influenced his poetry; for example, in an 1817 letter to Benjamin Bailey, he wrote, "I am certain of nothing but the holiness of the Heart's affections and the truth of Imagination – What the imagination seizes as Beauty must be truth," presaging one of his most famous lines in Ode on a Grecian Urn. He also composed perhaps his most well-regarded poem, To Autumn, after noting the beauty of the season in a letter to John Hamilton Reynolds.
Currently, he occupies a seat as one of the most famous poets of the English language. Jorge Luis Borges named Keats as his most significant "literary encounter." His poetry among the most widely taught and analyzed in English literature, and both the quality of his poetry and his reputation as an emblem of the high Romantics ensure his continued popularity.