John Keats was an English poet.
He was a poet who, according to Data, started a tradition of poets composing odes to individuals who had a profound impact on their life. (TNG: "Schisms")
Sometime prior to 2368, William T. Riker had received a bound copy of Keats' poem Ode to Psyche as a gift from Deanna Troi. (TNG: "Conundrum")
In 2372, Jake Sisko learned that Keats was helped in writing his works by Onaya, an entity who fed on his neural energy. This eventually killed him. (DS9: "The Muse")
This character was only mentioned in dialogue.
The comment Garak makes about Chalan Aroya's dress in "Broken Link" ("a thing of beauty is a joy forever") is from Book 1 of Endymion by Keats.
According to the Star Trek Encyclopedia (4th ed., vol. 1, p. 407), the birth and death years of John Keats were 1795 and 1821, respectively.