John Keats by Benjamin Robert Haydon
plaster cast of life-mask, 1816. © National Portrait Gallery, London. Reproduced under an academic licence.
John Keats by 
Monarch Notes on Keats' Poetry by 
This review of two books about Keats gives us some insight into both his literary techniques and the personal beliefs that shaped his writings. New Statesmen - How Keats lives on
Biographical information for John Keats via Britannica; this article also includes links to information about the Romantics, the various styles and techniques that Keats used in his poetry, and discusses the impact of his health on his work.
Romanticism - this article gives a thorough overview of the characteristics of Romanticsim in literature and other art forms, discusses the socio-political and cultural forces that brought about Romanticism, and which were themselves altered by the movement.
The Project Gutenberg eBook, Letters of John Keats to His Family and Friends, by John Keats, Edited by Sidney Colvin - read John Keats thoughts in his own words
Useful discussion of John Keats' background, influences upon his life, development as a poet https://www.poetryfoundation.org/poets/john-keats