Cai Lun was a Chinese eunuch who greatly reformed the art of papermaking. He was born in Guiyang (of today Hunan Province of Central China) during the Eastern Han Dynasty (25-220), and became a paperwork secretary; he was also assigned to the Shang Fang (imperial family's hand workshop) of Emperor Hedi.

At that time, although the technology of papermaking has already been invented, paper was used primarily among only common people. While most of the literati did not favor the paper, Cai saw the prospect of paper, which could substitute for silk. So Cai began to reform the papermaking technology

For papermaking, Cai earnestly summarized predecessors' experience and improved the technology .Cai first used bark to make paper, which largely enhanced the paper's output, because the dark material is richer than hemp.

Cai's paper (known as Cai Lun paper) was light and thin, strong and inexpensive, and could be mass-produced.

Cai's contribution is considered one of the most important inventions in history, since it enabled China to develop its civilization much faster than with earlier writing materials (primarily bamboo), and it did the same with Europe when it was introduced in the 12th or 13th century.