Carl Sagan's work was pretty much single handedly responsible for me finding any sort of direction in life. For most of my life before that I didn't have many passions outside of music and art, nothing I could confidently take forward as a career prospect. Eventually I accidentally stumbled upon his book
COSMOS through music message boards / online communities. The world through Sagan's lens was exactly what I needed at that point in my life, it was so unusually refreshing. My family was in a really dark place at the time, my brother was in and out of prison, my mother was in the process of dealing with drug addiction, my father was still bitter and lonely from a messy divorce several years earlier, and I was doing quite poorly in school. I desperately needed some sort of guidance and escapism, Sagan's books provided just that.
It was originally his commentaries on technological evolution and radio astronomy that provoked me to pursue electronics as both an academic interest and career. COSMOS pretty much did for me what The Bible does for Christians. I've read nearly all of Sagan's works since then, they are collectively by far the most influential books I've ever experienced.
The only other books that have come close were the many non-fiction works of Isaac Asimov and Howard Bloom's
Global Brain.