John Keats was an English Romantic poet who wrote many famous works, including the ODE (3 letters) and Endymion (8 letters). His most famous opus is a collection of his works, known as Keats' Opus. This collection includes some of his most renowned works, such as 'ODE to a Nightingale' and 'ODE on a Grecian Urn'. Keats' Opus is considered one of the most important collections of Romantic poetry in English literature.