How many astronauts have stood on Mars?

As of June of 2014, no astronauts have walked on the surface of the planet Mars. All of the space missions to Mars have been carried out by unmanned spacecraft.

The first successful unmanned mission to Mars was with the Mariner 4 spacecraft. It was launched on Nov. 28, 1964. It reached Mars on July 14, 1965, returning photographs of the planet. This was a passing flight, meaning that the craft did not actually land on the Mars; it just flew close enough to capture photographs of the terrain. On Aug. 6, 2012, a robotic space probe landed on the surface of Mars.