Final answer:
Annie Jump Cannon developed and reorganized the system of classifying stellar types for stars. She classified around 500,000 stars over her lifetime and her work served as a foundation for much of twentieth-century astronomy.
Step-by-step explanation:
The person who developed and reorganized the system of classifying stellar types for stars is Annie Jump Cannon. She was hired by Pickering as one of the "computers" to help with the classification of spectra. Cannon classified around 500,000 stars over her lifetime, classifying up to three stars per minute by looking at the stellar spectra. Her catalog of spectral types for hundreds of thousands of stars served as a foundation for much of twentieth-century astronomy.