Short answers, pulled from the story.
Helene was discovered by Pierre Laques and Jean Lecacheux in 1980 from ground-based observations at the Pic du Midi Observatory. The moon was initially catalogued as S/1980 S 6 before receiving its official name in 1988.
Helene is called a trojan moon because it occupies the leading Lagrangian point of Dione's orbit, where gravitational forces from Saturn and Dione hold it in a stable position ahead of the larger moon. It is one of only four known trojan moons in the solar system.
Cassini's closest documented approach to Helene occurred on the 3rd of March 2010, passing within 1,800 kilometers of the surface. Another successful imaging sequence took place in June 2011, with many additional passes over the course of the mission.
Helene's surface features broad depressions 2 to 10 kilometers across with interior slopes no greater than 12 degrees, thought to be decayed impact craters. The trailing hemisphere has roughly ten times more craters than the smoother leading hemisphere, and thin ridges 50 to 100 meters tall trace the slopes of many basins.
Helene's surface is snow-like, with particle sizes between 1 and 100 micrometers. At low packing densities the material behaves as a non-Newtonian Bingham substance, meaning it can flow plastically under stress in a way resembling candle-wax or glacial ice.
Helene was officially named in 1988 for Helen of Troy, a figure from Greek mythology. In that mythology, Helen was the granddaughter of Cronus, the deity the Romans knew as Saturn, making the name an appropriate choice for a moon of that planet.