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.
Mars Scout Program
The first robotic spacecraft in this program was "Phoenix", a lander originally intended for the canceled Mars Surveyor mission but adapted to the new mission. "Phoenix" was launched on August 4, 2007, and landed on the icy northern polar region of the planet on May 25, 2008. "Phoenix" was designed to search for environments suitable for microbial life on Mars, and to research the history of water there. The 90-day primary mission was successful and the overall mission was concluded on November 10, 2008, after engineers were unable to contact the craft. The lander last made a brief communication with Earth on November 2, 2008.