Original: The pug's popularity spread to Tibet, where they were mainly kept by Buddhist monks, and then went on to Japan, and finally Europe. The exact origins of the pug are unknown, as Emperor Qin Shi Huang, the first Emperor of China, destroyed all records, scrolls and art related to the pug at some point during his reign which lasted between 221 and 210 BCE.
Simplified: The pug's origin is unknown because the first Emperor of China destroyed everything related to the pug in his reign.