Chinese court official who is traditionally credited with the invention of paper.

Cai Lun was a eunuch who entered the service of the imperial palace in 75 CE and was made chief eunuch under the emperor Hedi (reigned 88–105/106) of the Dong (Eastern) Han dynasty in the year 89. About the year 105 Cai conceived the idea of forming sheets of paper from the macerated bark of trees, hemp waste, old rags, and fishnets. The paper thus obtained was found to be superior in writing quality to cloth made of pure silk (the principal writing surface of the time), as well as being much less expensive to produce and having more abundant sources.

Cai reported his discovery to the emperor, who commended him for it. Important improvements were subsequently made to Cai's papermaking process by his apprentice, Zuo Bo, and the process was rapidly adopted throughout China, from which it eventually spread to the rest of the world. Cai himself was named a marquess in 114.