When Pink Floyd was formed in 1965, Syd Barrett was its guiding star. His breakdown, characterized by many as "mental instability" but seeming more, in my amateur psychologist's opinion, as schizophrenia, self-medicated with LSD, had a huge effect on the band, their direction, and their music.
Syd's bright shining talent was honored by the band overtly on their incredible album "Wish You Were Here," and also in a practical way by their making sure that Syd continued to receive the royalties due to him. I suspect that Messrs. Gilmour, Mason, Waters, and Wright also gained more than a little sensitivity to mental illness from their experience with Syd.
Like Rimbaud, Syd Barrett had a longer life than actively and publicly creative period -- but a vast and lasting influence.