Alexander Skriabin (1871-1915)
For a time Skriabin tended to be viewed as a bit of an island as a Romantic composer, caught up in his own world of mysticism, using music and colour to bridge reality and divinity in a 'soliptic' language.
As a theosophist, Skriabin believed that one way of achieving a knowledge of God was via spiritual extasy from desire.
I love his music. The Poem of Extasy (1908), Prometheus: The Poem of Fire (1910) with its associated colour organ and the late symphonies, are transcendent. His piano music is deeply colourful with fluid harmonies that one can never quite fix.