Robert Pirsig, the author of Zen and the Art of Motorcycle Maintenance, died on Monday. He was 88. Pirsig, who had been institutionalised for a while after being diagnosed schizophrenic in the 1960s, died of natural causes, a statement issued by his publisher William Morrow & Co said.

Published in 1974 after being rejected by more than 100 publishers, Zen and the Art of Motorcycle Maintenance is a work of philosophical non-fiction and traces a father-son duo’s motorcycle journey across western United States. The book is believed to have been inspired by a 1968 motorcycle trip Pirsig undertook with this eldest son Christopher, who died in 1979.

The bestseller’s sequel Lila: An Inquiry into Morals was published in 1991 after Pirsig worked on it for 17 years. It is based on the voyage undertaken by two fictitious characters along the US east coast.

The author was a resident of South Berwick, Maine and is survived by his wife Wendy, two children and three grandchildren.