Franklin Ramón Chang-Díaz (born April 5, 1950, San José, Costa Rica) is an American mechanical engineer, physicist, and former NASA astronaut. He is the sole founder and CEO of Ad Astra Rocket Company as well as a member of the Cummins' board of directors. He became an American citizen in 1977.

He is a veteran of seven Space Shuttle missions, tying the record, as of 2021 for the most spaceflights (a record set two months earlier by Jerry L. Ross). He was the third Latin American, but the first Latin American immigrant NASA Astronaut selected to go into space. Chang-Díaz is a member of the NASA Astronaut Hall of Fame.