Who invented the "talking Patronus" spell used by the Order in the second Wizarding War?

Question

Read Order of the Phoenix again, and I thought of a question about the patronuses the Order uses. This "talking Patronus" spell seems to be an Order of the Phoenix invention, as I didn't notice anyone on the Dark Lord's side using it against the Order in the War.

Who invented the "talking Patronus" spell used by the Order in the second Wizarding War? I think it may have been Dumbledore, but does the author Rowling confirm that it really is Dumbledore who created this, in any book/interview/Pottermore-post or not?

Answer 1

Dumbledore

From Rowling’s old official site, jkrowling.com:

Members of the Order use their Patronuses to communicate with each other. They are the only wizards who know how to use their spirit guardians in this way and they have been taught to do so by Dumbledore (he invented this method of communication). The Patronus is an immensely efficient messenger for several reasons: it is an anti-Dark Arts device, which makes it highly resilient to interference from Dark wizards; it is not hindered by physical barriers; each Patronus is unique and distinctive, so that there is never any doubt which Order member has sent it; nobody else can conjure another person’s Patronus, so there is no danger of false messages being passed between Order members; nothing conspicuous needs to be carried by the Order member to create a Patronus.

However, it is worth keeping in mind that this information is from her old website. As such she may (as she has done on a few occasions) decide to change it in the future, such as by having Patronus communication in Fantastic Beasts, say.

Answer 2

There is no clear indication in the books that this use was invented by Dumbledore.

Here's what the Pottermore page on the Patronus Charm (written by J. K. Rowling) has to say (emphasis mine):

One of the most powerful defensive charms known to wizardkind, the Patronus can also be used as a messenger between wizards.

and

The Patronus Charm is one of the most ancient of charms and appears in many accounts of early magic.

The wording - "messenger between wizards" - and the charm being "ancient" leads me to conclude that the "messenger" use for it has existed as long as the charm itself.

Dumbledore is the first person to use it in the books:

“Should I go and get someone?” said Harry. “Madam Pomfrey?”

“No,” said Dumbledore swiftly. “Stay here.”

He raised his wand into the air and pointed it in the direction of Hagrid’s cabin. Harry saw something silvery dart out of it and streak away through the trees like a ghostly bird.
_{Harry Potter and the Goblet of Fire, chapter 28 "The Madness of Mr. Crouch", page 560, Scholastic.}

After that, there isn't much elaboration on the topic of the originator of this use of Patronus Charm. However, the following passage from Deathly Hallows suggests that the "talking Patronus" can be learned by means other than Dumbledore or members of the Order:

“Can you do that talking Patronus thing, then?” asked Ron.

“I’ve been practicing and I think so,” said Hermione.
_{Harry Potter and the Deathly Hallows, chapter 9 "A Place to Hide", page 164, Scholastic.}

That Hermione learned it by herself, with no explicit guidance from the members of the Order (though I don't deny that possibility), leads me to believe she learned it from a book, meaning that it has been documented, meaning that it must predate Dumbledore (since there's no indication Dumbledore ever published this feature of the Patronus Charm).

Voldemort's side doesn't use it because they don't need it.

Dementors are already their allies. The same page on Pottermore also indicates that most Dark Wizards consider Patronuses useless, though they can conjure them if needed (emphasis mine):

However, most [Dark Wizards], who become desensitised to the effects of the Dark creatures with whom they may ally themselves, regard the Patronus as an unnecessary spell to have in their arsenal.