Chang and Eng Bunker, Siamese-American showmen, the original conjoined twins (died 1874)

Chang Bunker and Eng Bunker were Siamese–American conjoined twin brothers whose fame propelled the expression "Siamese twins" to become synonymous for conjoined twins in general. They were widely exhibited as curiosities and were "two of the nineteenth century's most studied human beings".

Conjoined twins, popularly referred to as Siamese twins, are twins joined in utero. It is a very rare phenomenon, estimated to occur in anywhere between one in 50,000 births to one in 200,000 births, with a somewhat higher incidence in southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.

May 11 is the 131st day of the year in the Gregorian calendar; 234 days remain until the end of the year.