“Beauty is truth, truth beauty” - this is a quotation from the poem named:

John Keats, (born October 31, 1795, London, England—died February 23, 1821,Rome, papal list [Italy]), English Romantic lyric poet who devoted his short life to the perfection of a poetry marked by vivid imagery, great sensuous appeal, and an attempt to express a philosophy through classical legend.

John Keats was a romantic poet, who is also called ‘Poet of beauty’.

John Keats wrote:
- Ode to Psyche
- Ode on Melancholy
- To Autumn
- Bright Star
- On First Looking into Chapman's Homer
- Lamia
- The Eve of St
- La Belle Dame Sans Merci

Source: Britannica.com

“Beauty is truth, truth beauty” - this line occurs in Keats’s much celebrated poem ‘Ode on a Grecian Urn’