What Is the History of the Unforgivable Curses?

Question

What is the history of the Unforgivable curses?

‘Now ... those three curses – Avada Kedavra, Imperius and Cruciatus – are known as the Unforgivable Curses. The use of any one of them on a fellow human being is enough to earn a life sentence in Azkaban. That’s what you’re up against. That’s what I’ve got to teach you to fight. You need preparing. You need arming. But most of all, you need to practise constant, never-ceasing vigilance. Get out your quills ... copy this down ...’ [Mad-Eye Moody]

They spent the rest of the lesson taking notes on each of the Unforgivable Curses.

_{Goblet of Fire - page 192 - Bloomsbury - chapter 14, The Unforgivable Curses}

_{★ I'm looking for a canon-based answer (the Harry Potter novels, the three supplemental books, interviews with JKR, or Pottermore) and do not prefer an answer from either the HP Wikia or the Wikipedia.}

Answer 1

The Cruciatus, Imperius and Avada Kedavra Curses were first classified as Unforgivable in 1717, with the strictest penalties attached to their use.

Source: commentaries to Babbitty's tale in The tales of Beedle The Bard