History of the twin paradox
In special relativity, the history of the twin paradox chronicles the development of the famous thought experiment known as the twin paradox, which started in 1905 when Albert Einstein showed that a clock returning from a round-trip shows less elapsed time than a clock that remained at its place. By 1911, Einstein, Paul Langevin and Emil Wiechert had extended this result to life forms and human beings, with Hermann Weyl introducing twin brothers in 1918, see section § Round-trip experiment (1905).
Source: Wikipedia — History of the twin paradox (CC BY-SA 4.0)