The narrator of this puzzle is Doctor Harleen Quinzel, aka Batman villain Harley Quinn. Before she started working for the Joker (let's say this puzzle is mostly in the Batman: The Animated Series continuity), she was a psychologist who analyzed costumed villains at Arkham Asylum. Each note applies to a Batman villain, and the blanks below can be filled in with that villain's real name (as we assume they would appear in the asylum's files):
Some of these characters have had different "real names" in different continuities, but these are the originals, or, the most common, or, the most famous. Probably. I think.
The highlighted letters spell the answer, PHANTASM, as in the animated Batman movie Mask of the Phantasm. But the answer to the puzzle is not "ANDREA BEAUMONT."