Viking 1
Viking 1 was the first of two spacecraft (along with "Viking 2") sent to Mars as part of NASA's Viking program. On July 20, 1976, it became the second spacecraft to soft-land on Mars, and the first soft lander to successfully perform its mission. (The first spacecraft to soft-land on Mars was the Soviet Union's Mars 3 on December 2, 1971, which stopped transmitting after 14.5 seconds.) "Viking 1" held the record for the longest Mars surface mission of days (over 6¼ years) or Martian solar days, until that record was broken by "Opportunity" on May 19, 2010.
Luna 16
"Luna 16" was the first robotic probe to land on the Moon and return a sample of lunar soil to Earth after five unsuccessful similar attempts. The sample was returned from Mare Fecunditatis. It represented the first lunar sample return mission by the Soviet Union and was the third lunar sample return mission overall, following the Apollo 11 and Apollo 12 missions.