Li Siguang (Chinese: 李四光; pinyin: Lǐ Sìguāng; Wade–Giles: Li Ssu-kuang; 26 October 1889 – 29 April 1971), also known as J. S. Lee, was a Chinese geologist and politician. He was the founder of China's geomechanics. He was an ethnic Mongol. He made outstanding contributions, which changed the situation of "oil deficiency" in the country, enabling the large-scale development of oil fields to raise the country to the ranks of the world's major oil producers.