Chang (Chinese: 昌; pinyin: Chāng, Thai: จัน Chan) and Eng (Chinese: 恩; pinyin: Ēn, Thai: อิน In) Bunker (May 11, 1811 – January 17, 1874) were the conjoined twin brothers whose condition and birthplace became the basis for the term "Siamese twins".

The Bunker brothers were born on May 11, 1811 in Siam (now Thailand), in the province of Samutsongkram, to a fisherman and his wife (Nok or [Nak]; Thai: นาก). Because of their Chinese heritage (as they were born from a Thai Chinese father and a Chinese-Malay mother), they were known as the "Chinese Twins" in Siam. They were joined at the sternum by a small piece of cartilage. Their livers were fused but independently complete. Although 19th century medicine did not have the means to do so, modern surgical techniques would have easily allowed them to be separated.

In 1829, British merchant Robert Hunter discovered them and paid their family to be exhibited as a curiosity during a world tour. Upon termination of their contract with their discoverer, the brothers successfully went into business for themselves. In 1839, while visiting Wilkesboro, North Carolina, the twins were attracted to the area and settled on a 110-acre (0.45 km²) farm in nearby Traphill, becoming naturalized United States citizens.