Lishu originated in the Qin Dynasty and was compiled by Cheng Miao. It reached its peak in the Eastern Han Dynasty, which had a great influence on later calligraphy. Calligraphy is called "Tang Kai of Han Li".
What exactly is Li, and what is the strict difference from a seal? Xiao Zhuan retains the meaning of pictographic characters in order to paint its finished products; Lishu went further, breaking the knot of pictographs with stroke symbols and becoming pictographs of pictographs. In fact, seal script and official script are two systems, marking two major stages of the development of Chinese characters. Seal script is the end of pictographic ancient characters, and official script is the beginning of new words that turn pictographic characters into strokes.
For more information, please refer to the official script entry in Baidu Encyclopedia.