Short answers, pulled from the story.
Two separate teams of astronomers spotted Hyperion in September 1848. William Cranch Bond and his son George Phillips Bond worked in the United States while William Lassell observed from the United Kingdom.
Hyperion has a highly irregular shape that resembles a giant sponge with about 40 percent empty space. Its low density indicates it consists mostly of water ice with very little rock mixed in.
The moon remains the only regular planetary natural satellite known not to be tidally locked due to its irregular shape and eccentric orbit. Proximity to the much larger moon Titan plays a critical role in this instability along with a 3:4 orbital resonance.
Cassini conducted five close targeted flybys of Hyperion during its mission timeline spanning ten years. The first encounter occurred on the 25th of September 2005 and the final flyby took place on the 31st of May 2015.