William Gun Chong BEM (Chinese: 鄭根; 1911–2006) was a Canadian spy who served in the British Military Intelligence unit MI9 during World War II.

He escaped to free China where he joined the British Army Aid Group, a paramilitary unit of MI9.

Chong then was a British spy, known as Agent 50, who operated behind Japanese lines in occupied China.

The people Chong smuggled were British and Commonwealth subjects and stranded Allied aviators.

Chong did not recognize two of his charges as the chief justice and prosecutor of Hong Kong, until after the war when he was called as a witness in a trial of a collaborator.