NASA’s Viking 1 became the first spacecraft to land successfully and operate on Mars.
Viking 1 entered Mars orbit on June 19, 1976, and its lander touched down in Chryse Planitia on July 20, 1976. The mission carried both an orbiter and a lander. The orbiter photographed the planet from above, while the lander analyzed soil, weather, and the local surface environment.
The lander transmitted its first image shortly after landing and continued working far longer than its planned primary mission. It returned panoramic photographs, temperature and wind measurements, and results from biology experiments designed to test whether Martian soil showed signs of microbial activity. Those experiments produced intriguing chemical reactions, but no widely accepted evidence of living organisms.
Viking 2 landed successfully later in 1976 at Utopia Planitia. Earlier probes had reached Mars, but several had failed during landing or soon afterward. Viking 1 is therefore specifically remembered as the first successful operational landing mission, not simply the first probe to approach Mars.