Fictional spies aren't restricted to stories in more modern times, filled with gadgets and acronyms. There are also spies in traditional sword and sorcery fantasy. Of all those creations, the best one is the entire country of Drasnia in David Eddings' The Balgariad and its sequels, prequels, and side works.
David Eddings' books are designed to follow as many fantasy tropes as humanly possible, while also being well-written and gloriously fun. And one of the tropes is that each nation of that world has a very specific set of characteristics. Like many creation myths, there are deities of greater power who create the world and ones that are given dominion over the resulting earth. In these books, there are seven lesser gods, and the people who follow them all take on characteristics prized by their god.
The Nyssans have Issa, the snake god and they're all poisoners and assassins. The Tolnedrans have Nedra and they're all about gaining imperial might and money. The Arends have Chaldran and they're all knights and archers of the medieval fantasy persuasion — lots of courtly love and honor. The Marags have Mara, and they ended up mostly wiped out. And the Angaraks have Torak, an evil god whose people are divided into groups with their own characteristics — power-mad, human sacrifice priests, bureaucrats, fighters, and merchants.
But the ones we're concerned with here are the Alorns, whose god is Belar. Like the Angaraks, they have several kingdoms, each with a troperiffic identity. Chereks are seafaring ship-masters. Algarians are nomadic horse people. Rivans are basically practical people who were charged with living on an island guarding a sacred orb. And the last one is the one we're concerned with here: Drasnians. Drasnians are spies. All of them. There are likely people who are less spy-inclined than others — you can't have a nation of only spies, they are also merchants. Merchants that everyone assumes are really spies. And Eddings makes Drasnian spying look fun.
Drasnia's most prestigious school? A spy academy. Their king? Spymaster. Their castle? Filled with spyholes. This is spycraft as national pastime. The books spend the most time with Silk, who is a prince and the companion of the traditional chosen one. He's called Silk because graduates of the spy academy get code names that are more like nicknames. They all clearly prefer them to their real names. Silk's a prince who much prefers his status as a brilliant spy to his aristocratic one. Silk routinely refers to what he does as a "game," one you win by coming out on top. While the Tolnedrans want money out of greed, Silk explains the Drasnian outlook with "The money's just a way of keeping score. It's the game that's important."
Spying in Drasnia is also source of national pride. These are not people who see spying as a underhanded necessity, this is what they do. Even among friends. The king of the Drasnians, Rhodar, once explains spying on his own allies as it being easier:
"Could you penetrate this palace, Prince Kheldar?" King Anheg challenged.
"I already have, your Majesty," Silk said modestly, "a dozen times or more."
Anheg looked at Rhodar with one raised eyebrow.
Rhodar coughed slightly. "It was some time ago, Anheg. Nothing serious. I was just curious about something, that's all."
"All you had to do was ask," Anheg said in a slightly injured tone.
"I didn't want to bother you," Rhodar said with a shrug. "Besides, it's more fun to do it the other way."
The other great thing about Eddings' creation is how much thought is put into how this society, where you literally can't trust anything, actually functions. The same skills that work for spies work for merchants, and that's how the society sustains itself. The reputation of the Drasnian service is such that the official policy following the death of one of their agents is assassination and terror. They assume there are spies everywhere, and that they can read lips, so they have a second, secret sign language.
The code name as real name thing makes sense, too. All the spies have a raft of different identities they use when it suits them, so of course their spy identity is the "real" one. Silk becomes a successful merchant, with the trappings to match, but he sloughs off "Prince Kheldar" as soon as he needs to.
There's also a moment where the queen, seeing a loophole in how the official spies leave her alone when she's nursing her child, has the official spymaster dress as a lady's maid so they can talk in peace. And her husband, used to the twisty thinking of running a literal country of spies, turns out to be the best tactician of all. That's the kind of thinking required of Drasnians.
And all of that — along with Drasnians consistently being the wittiest in a very humor-inclined series — makes them the best spies in fantasy.