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.
NASA robots
The Mars rover "Curiosity" is a mobile laboratory that was launched from Cape Canaveral in 2011. The Curiosity landed on Mars surface August 6, 2012. This was the largest rover NASA has put on Mars, being twice as long and five times as heavy as its processors. Despite the extra size the Curiosity took many design elements from the previous generation of Mars rovers such as six wheel drive, rocker-bogie suspension, and cameras mounted to the mast of the rover to help the mission's team direct the rover. However unlike the previous generation the Curiosity contains an entire inboard laboratory for analyzing the soil and rocks on Mars. NASA engineered the Curiosity to be capable of rolling over obstacles up to 65 centimeters high and traverse up to about 200 meters per day on Martian terrain. Curiosity got its electrical power from a Radioisotope thermoelectric generator.