Byron and Keats

'You speak of Lord Byron and me - There is this great difference between us.
He describes what he sees - I describe what I imagine - Mine is the hardest task.'
John Keats in a letter to his brother George, September 1819.

The rivalry and dislike between George Gordon Noel Byron, 6th Baron Byron, and John Keats has been much discussed; in their own time, however, it was felt far more keenly by Keats. Byron was a flamboyant and handsome nobleman whose wit, charm and ancestral title accorded him entry into the most elite circles of English society. He was also an accomplished and celebrated poet. His first major work, 'Childe Harold's Pilgrimage', was a great success and he enjoyed all the attendant benefits of celebrity. John Keats was a poor and struggling middle-class poet whose work was often savaged by the great critics of the age; he was advised that poetry was the provenance of nobleman such as Byron, and dismissed (by Byron, among others) as a 'Cockney' poet.
The animus between Byron and Keats is easy enough to explain. Byron was a snob, though he occasionally rose above such petty social concerns. He also revered the 18th century Augustan poets, particularly Alexander Pope, whose adherence to the classical tradition is echoed in his own early poetry. Keats's work was deeply at odds with the Augustans; also, his 'Sleep and Poetry', which Byron read, was critical of their work. Keats found inspiration in the extravagant and sensuous wordplay of the 16th century and also admired the works of Wordsworth and Coleridge. Those first generation Romantics poets had caused a literary revolution with their rejection of Augustan classicism. And so, quite simply, Byron disliked Keats's poetry on an aesthetic level. Keats felt likewise about Byron's work; he considered it overrated, slavish and unoriginal. It was a sort of reverse snobbery.
And there is also the simple envy Keats felt over Byron's success. As he was forever beset by financial concerns, his jealousy is understandable enough. It was exacerbated by his belief that Byron succeeded only because he was an aristocrat who catered to an undemanding audience ('You see what it is to be six foot tall and a lord!', Keats remarked to a friend upon reading a favorable review of Byron's work.)
But it is worth remembering that Byron came to recognize Keats's talent. He also scoffed at the notion that anyone would be so sensitive as to die because of bad reviews (he himself was savaged more than once.) In this respect, Byron had more insight into Keats's character than those who should have known him far better.