A Costa Rican-American engineer, physicist and former NASA astronaut, one of the first Hispanic Americans to go into space and the first naturalized U.S. citizen to become an astronaut.
He is a veteran of seven Space Shuttle missions, making him the record holder as of 2008 for the most spaceflights, a record he shares with Jerry L. Ross.
His father was of Chinese descent and his mother a Spanish Costa Rican.
He studied in high schools in both Costa Rica and the United States. He earned a B.S. degree in mechanical engineering from the University of Connecticut in 1973, and a Sc.D. degree in applied plasma physics from the Massachusetts Institute of Technology in 1977.
He was selected as an astronaut candidate by NASA in 1980 and his first Shuttle flight was in 1986.