The term "Siamese twins" came from Eng and Chang Bunker
The “original” conjoined twins whose lives coined the phrase “Siamese twins” were Eng and Chang Bunker. The brothers were born in Siam (now Thailand) in 1811 and miraculously lived to age 63. In 1829, when they were 17, Eng and Chang were taken to America by two men who saw a money-making scheme in the brothers. Setting them up as a freak show, Eng and Chang were treated like slaves while people paid their “owners” admission to see the phenomenon of these conjoined siblings.
After some time, however, the two were able to negotiate their freedom and eventually bought land with their savings in Mount Airy, North Carolina. There, the two ironically bought slaves to work on their farm. Eng and Chang later met and married two sisters and fathered a total of 21 children between the two of them. An autopsy performed after their death in 1874 revealed they shared a liver, which is now on display at the Mutter Museum in Philadelphia, Pennsylvania.