Chum Jian

 was a Chinese man who came from Shanghai to California with his brothers to mine for gold.

Chum's brothers became possessed by an alien after drinking watered-down whiskey. Chum was unaffected because he didn't drink whiskey. He told his story to the Sixth Doctor, who used this information to free not only the possessed men but also the alien as well. (PROSE: Whiskey and Water)