Short answers, pulled from the story.
Apollo-Soyuz was the first crewed international space mission, conducted jointly by the United States and the Soviet Union in July 1975. An American Apollo spacecraft docked with the Soviet Soyuz 19 capsule on the 17th of July 1975, and the two crews spent 1 day, 23 hours, 7 minutes, and 3 seconds docked together.
The American crew consisted of Thomas P. Stafford (commander), Vance D. Brand, and Deke Slayton. The Soviet crew was Alexei Leonov and Valery Kubasov. Slayton was one of the original Mercury Seven astronauts, selected in April 1959, but had been grounded for medical reasons until 1972.
Apollo-Soyuz was a symbolic act of detente between the United States and the Soviet Union at a time of deep rivalry. Soviet leader Leonid Brezhnev described it as the first major joint scientific experiment in history, framing it as a statement that the planet was too small to be threatened by nuclear war. The mission set a precedent for the later Shuttle-Mir program and the International Space Station.
During reentry and splashdown, the Apollo crew was accidentally exposed to toxic monomethylhydrazine and nitrogen tetroxide fumes from the reaction control system, which had been left on during descent. Vance Brand briefly lost consciousness; Stafford retrieved emergency oxygen masks for all three. All three astronauts were hospitalized for two weeks in Honolulu, Hawaii.
Engineer Bill Creasy designed the Androgynous Peripheral Attach System (APAS) for the mission, allowing either spacecraft to be active or passive during docking. A derivative version, APAS-89, was later used for the Shuttle-Mir program beginning with STS-71 twenty years later. The first Pressurized Mating Adapter using APAS lineage hardware remains in use on the International Space Station as of 2024.
The Apollo spacecraft carried the SAG telescope, which discovered two ultraviolet sources, HZ 43 and FEIGE 24, both white dwarfs. The crew also maneuvered Apollo to create an artificial solar eclipse so Soyuz instruments could photograph the solar corona. Embryologist Jane Oppenheimer analyzed the effects of weightlessness on fish eggs at various stages of development.