Titan ( or Saturn VI) is the largest moon of Saturn discovered by Christiaan Huygens in 1655. It is named after the Titans of Greek mythology. It is the only known natural satellite to have a dense atmosphere and the only object other other than Earth to have clear evidence of liquid on its surface. Titan has a yellow colour because of an organonitrogen haze. It is the second biggest moon in the solar system after Ganymede and its larger by volume than Mercury but has less mass.
Titan is primarily composed by water ice and rocky material. Its opaque atmosphere prevent examining of its surface without a probe. The Cassini mission sent a probe and found liquid bodies of liquid methane and its surface is young and smooth with some mountains and possible cryovolcanoes. It has a methane cycle similar to our water cycle and may host microbial life or at least be a prebiotic environment with complex chemistry on the surface with a possible biotic ocean in its subsurface. Its surface temperature is 93.7 kelvin or -179.5 degrees Celsius.
Pic courtesy: Wikipedia. References: Wikipedia and lectures on Coursera by Prof Charles Cockell of the University of Edinburgh.