Short answers, pulled from the story.
Proteus was discovered from images taken by the Voyager 2 space probe approximately two months before its Neptune flyby in August 1989. Stephen P. Synnott and Bradford A. Smith announced the discovery on the 7th of July, 1989, based on 17 frames taken over 21 days, placing the actual sighting before the 16th of June.
Proteus is about 420 km in diameter, making it the second-largest moon of Neptune and the largest of Neptune's inner regular moons. It is larger than Nereid, Neptune's third-largest moon.
Proteus orbits Neptune at a distance of approximately 117,647 km, so close to the planet that it is lost in the glare of reflected sunlight. No Earth-based telescope could separate it from Neptune's brightness; only the close approach of Voyager 2 in 1989 revealed it.
The largest crater on Proteus is Pharos, which measures 255 plus or minus 12 km in diameter and is approximately 10-15 km deep. It has a central dome on its floor and is the only officially named surface feature on the moon, approved in 1994 and named after the island where the god Proteus reigned and after the Lighthouse of Alexandria.
The surface of Proteus is dark, with a geometrical albedo of about 10 percent, and shows signs of complex organic compounds such as hydrocarbons or cyanides in the near-infrared range. James Webb Space Telescope NIRCam spectrophotometry has also detected a 3-micrometer absorption feature suggesting possible water ice or hydrated minerals on the surface.
Proteus is believed to have formed from debris produced after Neptune's large moon Triton was captured into orbit. Triton's initial highly eccentric orbit caused chaotic collisions among Neptune's original inner moons, reducing them to a rubble disc. Once Triton's orbit circularized, Proteus accreted from that rubble, starting about 8,000 km closer to Neptune than its current position before migrating outward through tidal interactions.