It’s almost Halloween and I’ve been thinking of that stereotypical witch’s laugh and the evil scientist diabolical laugh and was wondering how that began, whether that’s cinema or in literature before that.
He laughed the bony child to scorne
That was the bonny Lord of Learne.
He laughed that bonny boy to scorne;
Lord! pitty it was to heare;
We don't know, exactly. We do know that it is a very old trope, and has many variations. The idea of the "evil laugh" or "wicked laugh" is probably as old as literature, with the idea that someone is taking amusement at something wrong. To give one early example:
He told me this was the worst ball for company there had been the whole season; and, with a wicked laugh that was too significant to be misunderstood, said, "And, as you have been to no other, perhaps you will give this for a specimen of a Bath ball!"
The idea of the "evil laugh" changed a bit in the contemporary period as psychology changed attitudes towards behavior, and this is the origin of the "maniacal laugh." The "maniac" in this case could be a murderer or other criminal, but it became especially associated with the stock character of the "mad scientist." You can see its origins in the bouts of maniacal energy expressed by Victor Frankenstein in Mary Shelley's novel:
We ascended into my room, and the servant presently brought breakfast; but I was unable to contain myself. It was not joy only that possessed me; I felt my flesh tingle with excess of sensitiveness, and my pulse beat rapidly. I was unable to remain for a single instant in the same place; I jumped over the chairs, clapped my hands, and laughed aloud. Clerval at first attributed my unusual spirits to joy on his arrival, but when he observed me more attentively, he saw a wildness in my eyes for which he could not account, and my loud, unrestrained, heartless laughter frightened and astonished him.
“My dear Victor,” cried he, “what, for God’s sake, is the matter? Do not laugh in that manner. How ill you are! What is the cause of all this?”
In the 1931 film Frankenstein, this kind of activity was translated to the gleeful declaration "It's alive, alive!" and you see similar such character in cinema in Dr. Meirschultz in Maniac (1934). In these cases, the laughter verges from merely inappropriate (laughing at odd times, as by a secret jest or an inability to control ones actions) to actively "evil."
This should be distinguished from uncontrollable laughter as a genuine symptom of mental illness, which is often called paradoxical laughter and was generally associated with individuals who were, because of stress, trauma, or some other factor emotionally unstable. You can still see this kind of laughter-as-a-symptom-of-mental-illness in the character of the Joker in the Batman franchise.
Related to this there is also the "spooky laugh," which is usually characterized by laughter being unexpected and out of place, or of a particular frightening character. For example in Edgar Allan Poe's "A Cask of Amontillado":
But now there came from out the niche a low laugh that erected the hairs upon my head.
Most evil laughs as we know them today probably originated from the theater, because it was these traditions that led into the early radio and film affectations. A very notable "chilling laugh" was that on The Shadow radio program in 1930. The pulps were replete with examples of weird laughter of all kinds, and you sometimes get phonetic renderings like "Ha! Ha! Ha!" but the really invented phonetic display of them came in comic strips and comic books.
The witches' cackle is a harder one to pin down. In 1939 The Wizard of Oz film, the Wicked Witch of the West's distinctive gloating cachinnation being one example; a lot of her depiction wasn't exactly new or unique, but it was distinctive and influenced many subsequent depictions of witches. The book, The Wonderful Wizard of Oz does specify that the Wicked Witch laughs, but it's never described explicitly as an evil laugh or a cackle. You might compare this with the witch's laugh in Snow White and the Seven Dwarfs (1937).
So it's definitely a literary trope that spread out into different media and took different forms and established traditions as it spread.
I also will laugh at your calamity;
I will mock when terror strikes you,