The Hitchhiker's Guide to the Galaxy — Douglas Adams (1979)

Douglas Adams's comedic masterpiece began as a BBC radio play before becoming one of the best-loved novels in the English language. It combines genuinely funny comedy with surprisingly deep philosophical observations about the nature of existence, meaning, and bureaucracy. "42" (the answer to life, the universe, and everything) and the Babel Fish's proof of God's non-existence are among literature's most enduring comedic philosophical constructs.