Which NASA robot spent 14 years operating on Mars after landing in 2004?

The NASA robot that spent 14 years operating on Mars after landing in 2004 was the Opportunity rover.

Opportunity landed in Meridiani Planum on January 25, 2004, shortly after its twin rover Spirit arrived on the opposite side of Mars. NASA initially designed both vehicles for missions lasting about 90 Martian days, but Opportunity continued working far beyond that expectation. It investigated rocks, soil, craters, and geological features that provided evidence of ancient water activity.

A major milestone came when Opportunity reached the rim of Endeavour crater, a large impact crater it studied for years. The rover also traveled farther across the surface of another planet than any other vehicle at the time. A planet-wide dust storm in 2018 blocked sunlight from reaching its solar panels, and NASA declared the mission complete in February 2019.

Opportunity is sometimes confused with Spirit because both were launched as Mars Exploration Rovers in 2003. Spirit stopped communicating in 2010, while Opportunity continued until 2018.