Dante I and Dante II are two robots developed by Red Whittaker at the Robotics Institute at Carnegie Mellon University. The Dantes, currently retired, got their name from their task -- to descend into and explore active volcanos. (Get it? Descending into big, fiery volcanos, kind of like descending through the levels of Hell in Dante's Inferno?)
Physically, the Dante robots are eight-legged walking robots, connected to the outside of the volcano by a tether to allow rappelling. Their instrumentation allows them to sample and measure volcanic gases.
In 1994, Dante II successfully explored Mt. Spurr in Alaska. Dante I, however, met with a more embarrassing (from the perspective of the researchers) fate. During the onsite demonstration, Dante I lost its foothold and fell into the volcano. Although it was rescued by the use of it's tether, it was retired and never successfully completed it's task.
For more information on the Dante projects, you can check out the project website at www.ri.cmu.edu/projects/project_163.html