Short answers, pulled from the story.
Hyperion was discovered in September 1848. It was found independently by William Cranch Bond and George Phillips Bond in the United States, and by William Lassell in the United Kingdom at nearly the same time.
Hyperion's sponge-like appearance results from its unusually low density and high porosity, with about forty percent of the moon being empty space. Its weak surface gravity means impactors compress the surface rather than excavating it, and most ejected material never returns, leaving deep, sharp-edged craters permanently intact.
Hyperion's chaotic rotation is driven by its highly irregular shape, its eccentric orbit, and its gravitational interaction with the much larger nearby moon Titan, including a 3:4 orbital resonance. Its axis wobbles so severely that its orientation in space is unpredictable, with a Lyapunov time of around 30 days.
Hyperion is composed largely of water ice with only a small amount of rock. Its physical structure resembles a loosely packed pile of rubble, with a porosity of about 0.46. A thin layer of dark reddish material, containing long chains of carbon and hydrogen, coats its surface.
Both Voyager 2 and the Cassini orbiter observed Hyperion. Cassini made its first close targeted flyby on the 25th of September 2005 at 500 kilometers, with additional close approaches on the 25th of August 2011, the 16th of September 2011, and a final flyby on the 31st of May 2015.
Hyperion is the only regular planetary natural satellite known not to be tidally locked, and one of only a few moons in the solar system with a confirmed chaotic rotation. It was also the first non-rounded moon ever discovered, and its surface is electrically charged, a property not confirmed on any moon other than Earth's Moon before Hyperion.