What did Hugo Baskerville do to cause the curse of the Baskerville Hound?

In Chapter Two, Dr. Mortimer first reads the maniscript, given to him by Sir Charles, to Holmes and Watson. The writer of the story identifies himself as a Baskerville, explaining that this legend has been passed down in his family over several generations. During the Great Rebellion (around the mid-1600s), the Baskerville estate was owned by Hugo Baskerville, a "wild, profane, and godless man" (146). When one young woman refused to return his advances, he trapped her an upper chamber of his house. She escaped one night while Hugo was entertaining friends, and Hugo declared that he would give his body and soul to "the Powers of Evil" if he could find her (147). One man suggested that they set the hounds after her, and Hugo took his advice before chasing her out into the moor on his black mare.

Thirteen men followed Hugo, who was ahead of them. They encountered a shepherd who was "crazed with fear" - he had seen the maiden, but had also seen a "hound of hell" in fast pursuit of Hugo (148). Eventually, the men encountered Hugo's mare, alone and frothing at the mouth. Frightened, they persevered until they came across a trench, next to which the hounds were whimpering. In the trench, three of the men found the maiden, dead "of fear and of fatigue", and Hugo, dwarfed by a "great, black beast, shaped like a hound" (148). The giant hound tore Baskerville's throat out, at which point the men fled. One of the men died that night, while the other two remained "broken men" for the rest of their days (149).

The writer concludes his story by insisting that the hound has plagued the Baskerville family even since, and warns his sons to never cross the moor at night.