DENDRAL, whose development began in 1965 at Standford University at the request of NASA.
NASA was planning to send an unmanned spacecraft to Mars and wanted a computer program that could perform chemical analysis of the Martian soil.
Given mass spectral data of the soil, the program needed to determine its molecular structure.
The pioneering work on DENDRAL led AI researchers to realize that intelligent behavior is dependent not so much on the methods of reasoning as on the knowledge one has to reason with.