These spectra were created by Mike Briley, University of Maryland in the late 1980's. They are synthetic spectra computed by the synthetic spectrum FORTRAN code SSG which is due to Roger Bell, also University of Maryland. The spectra are "relative flux" spectra, which removes the very strong variation in the overall flux balance between Early type, hot, stellar spectra at the top of the figure, and the Late type, cool, stellar spectra at the bottom. In real life, the hot stars have most of their flux in the blue part of the spectrum, while the cool ones are very red.
Enjoy the view and watch how some different dark absorption lines and molecular bands vary in strength with stellar effective temperature.