Who is best known for ‘symbolism and mysticism’?

Yeats’s mythology, from which arises the distilled symbolism of his great period, is not always easy to understand, nor did Yeats intend its full meaning to be immediately apparent to those unfamiliar with his thought and the tradition in which he worked. William Butler Yeats, (born June 13, 1865, Sandymount, Dublin, Ireland—died January 28, 1939, Roquebrune-Cap-Martin, France), Irish poet, dramatist, and prose writer, one of the greatest English-language poets of the 20th century. He received the Nobel Prize for Literature in 1923. Some of his literary works: The Wild Swan at Coole, The Tower, The Winding Stair and Other Poems, Byzantium etc. Source: britannica.com