A brown dwarf is an object that is more massive than a planet like Jupiter, but not massive enough to undergo sustained nuclear fusion like a star. For many years they existed only in theory, as they had not been found in nature.
All of that changed in 1994 when a team of astronomers using Palomar's 60-inch telescope (armed with an early form of adaptive optics) captured the first image of one:
The big blob in the image is a dwarf star known as Gliese 229. The smaller blob to the right is Gliese 229B, the first brown dwarf discovered. The discovery was confirmed just over a year later by the Hubble Space Telescope.