The lore states that heroes travelled to Tristram after the events that led Leoric to madness.
"[...] hearing rumors of a corrupting evil, vast riches, and arcane magic."
More specifically, Aidan was a warrior, and returned to these events after fighting in the war against Westmarch.
Upon returning to Tristram and seeing his father raised from the dead, his younger brother missing and Lazarus gone, he journeyed into the depths of the labyrinth under the Cathedral.
Is there any evidence that these heroes had experienced any of these kinds of creatures before the events of Tristram?