Rand al’Thor was found as a baby on the slopes of Dragonmount and taken to Two Rivers, where he grew into a broad-shouldered shepherd boy. But Rand is possessed of immense power, a power as yet untapped, for he is also The Dragon Reborn, destined to be hunted by Darkhounds and Darkfriends as he bids to prove himself a mighty warrior leader. Among other things, Rand’s existence shows that you should always believe ancient prophesies, that even the low-born can save the world – and that characters in TV fantasy series must always have two names.

Rand is just one of the 2,782 characters who appear in Wheel of Time, the bestselling saga of fantasy novels by Robert Jordan. We can only hope the forthcoming adaptation on Amazon will hone the cast down a little, as we follow Rand and his forces towards Tarmon Gai’don, or the final battle between good and evil.

We’re going to see a lot of Rand and his like over the next few years, thanks to the all-slaying success of Game of Thrones, which returns for its final series this month and then is no more. TV executives, aware for some time that the enormous appetite for fantasy series will not disappear after the Iron Throne has seated its final backside, have been raiding the bookshelves for weighty tomes to take on.

Supernatural monster-hunter … Henry Cavill as The Witcher. Photograph: Netfilx

With Netflix adapting The Witcher, the cult series by Andrzej Sapkowski about supernatural monster-hunter Geralt of Rivia, and Amazon making big-budget plans for a new take on JRR Tolkien’s Lord of the Rings, the years ahead are going to be dominated by a genre previously belittled, mocked or ignored.

“Game of Thrones didn’t just open the door to more fantasy commissions,” says US TV critic Maureen Ryan. “It opened the floodgates. I honestly believe that the two biggest things to happen to TV in the last decade were the runaway successes of Game of Thrones and The Walking Dead. It told TV executives not just to pursue fantasy books or comics – but to gobble them up.”

The gobbling shows no sign of stopping. In addition to Witcher, Netflix has signed a deal with CS Lewis’s estate for The Chronicles of Narnia, and is also adaptating Leigh Bardugo’s Grishaverse novels whose hero, in an inversion of the standard fantasy trope, is a heroine. Her coming-of-age journey is not as straightforward as it initially seems, though she does of course have two names: Alina Starkov and the somewhat grander Sun Summoner.

US channel Showtime is working with Lionsgate on both a film adaptation and a TV spinoff of Patrick Rothfuss’s acclaimed Kingkiller Chronicle, which also subverts fantasy tropes, showing the protagonist not as a shining hero but as a guilty and broken man. On board as producer is Lin-Manuel Miranda, creator of musical phenomenon Hamilton. Meanwhile, in one of the few original projects in development, Joss Whedon will return to TV with The Nevers, a slice of Victorian sci-fi to air on HBO.

We have HBO to thank for something that sounds genuinely groundbreaking: it has optioned Nnedi Okorafor’s Who Fears Death, which is set in a beautifully drawn post-apocalyptic Sudan and follows Onyesonwu, a child born of rape, on her quest for revenge against her sorcerer father. HBO, keen to keep the goose laying its golden eggs, will also begin filming Long Night, the Game of Thrones prequel, this summer, with Naomi Watts heading the cast and a script by Jane Goldman, co-writer of 2010’s glorious superhero riot Kick-Ass.

Into this crowded arena comes the BBC with its ambitious take on Philip Pullman’s His Dark Materials due to air later this year. A recent trailer, showing glimpses of everyone from spirited heroine Lyra to glamorous villain Mrs Coulter, all but broke the internet. And spring will see the long-awaited arrival on Amazon of Good Omens, Neil Gaiman’s adaptation of his and Terry Pratchett’s much-loved novel about an angel and demon who join forces to try to save the world. The book’s subtitle is: The Nice and Accurate Prophecies of Agnes Nutter, Witch.

“Where Game of Thrones has changed things,” says Gaiman, “is not so much in the acceptance of fantasy as in the acceptance of budget. When the idea of making Good Omens first came up, I knew I didn’t want to make the cheap kid brother to Game of Thrones. Amazon understood that and were supportive. The game-changer isn’t really the fantasy bit so much as the idea that you can make TV at that budget and it can be a serviceable business model.”

The people running studios grew up on fantasy – and they want to put what they love on screen Neil Gaiman

Gaiman, whose cult novel American Gods was also adapted by Amazon, feels this change in attitudes to fantasy is as much generational as it is driven by Game of Thrones. “The thing that has fascinated me most is that, all through the 90s and early 2000s, people would tell me fantasy doesn’t sell. I would tell them that wasn’t true because the top 20 movies even then were all fantasy and sci-fi. They’d spend a lot of time telling me why they didn’t count. Now when I go in for meetings, the people running the studios grew up on fantasy. They’re not embarrassed about that and they’re happy to put what they love on screen.”

If Game of Thrones has taught us anything, it’s that what a significant number of viewers love is stories of madness and magic set in a world of high stakes and low morals. Filled with dragons and demons, yes, but also with fully realised worlds, strong characterisation and, most importantly, witty scripts.

Cameron Roach is head of drama for Sky, which recently had a word-of-mouth hit with Deborah Harkness’s A Discovery of Witches, about a historian-witch who makes an uneasy alliance with a suave vampire. “Where once people might have been dismissive of this genre,” says Roach, “what we’re seeing is that, increasingly, there are no rules as to what you should or shouldn’t commission.”

Druid magic … Mackenzie Crook in Britannia. Photograph: Victoria Etaghene/Sky UK Ltd

Roach stresses that striking the right tone is important, mentioning Britannia, playwright Jez Butterworth’s psychedelic take on early British history that saw a pointy-toothed McKenzie Crook playing the sort of druid you’d run a mile from. “[Britannia] has a unique voice,” says Roach, “and there are people who absolutely respond to that, who love the more fantastical elements. A lot of people didn’t come to Game of Thrones until the third series. We’re seeing TV companies making a long-term commitment to shows because they know they can grow their audiences. We’re interested in content that will still be being consumed in five to 10 years’ time. Fantasy is an important component of that.”

Not everyone is convinced that simply raiding the fantasy shelves will guarantee a dragon-sized hit. Among them is Adam Whitehead, who runs sci-fi and fantasy blog The Wertzone. “After the success of Peter Jackson’s Lord of the Rings films,” he says, “it was assumed we’d get lots of hit epic fantasy movies. Instead we got a bunch of bombs.” He singles out two: flat-footed dragon saga Eragon, and The Golden Compass, which asquashed every bit of wonder out of Pullman’s tale. “There were only a couple of so-so successes, such as the Narnia movies, before the genre lost its shine and cinema moved on to superheroes and dystopian YA. The question here will be if Game of Thrones was a one-off success or if it has sparked a wider audience interest in fantasy TV.”

Lacklustre … MTV’s The Shannara Chronicles. Photograph: MTV

While it’s true that the number of fantasy shows being commissioned is increasing, their quality remains at best mixed. For every Discovery of Witches, there is a Shannara Chronicles, MTV’s lacklustre take on Terry Brooks’ much-loved swords and sorcery saga, or The Bastard Executioner, an ultra-violent tale of medieval mayhem that had the blood and gore of Game of Thrones but none of its character development and wit.

“It’s not enough to have swords, mystical elements and dozens of burly men with unkempt beards,” says critic Ryan. “It’s worth remembering that HBO didn’t just want to put a fantasy drama on the air – it wanted to put a good fantasy on air. It spent years of development on Game of Thrones, filming, recasting, reshooting and tweaking, making it as good as it could be well before it premiered. There’s something of a land-grab mentality right now on TV, a feeling that people are just flinging something out there to stay in the game.”

There's something of a land-grab mentality right now, a feeling that people are just flinging something out there

Could this apply to Lord of the Rings, rumoured to have cost Amazon $250m (£190m) for a five-series deal? Season one, which reportedly has a bigger budget than the original film’s, remains shrouded in secrecy. Studio head Jennifer Salke recently outlined just how secretive, telling the Hollywood Reporter: “There’s a fantastic writers’ room working under lock and key. You have to go through clearance, and they have all their windows taped closed. There’s a security guard that sits outside and you have to have a fingerprint to get in.”

Ryan, for one, remains unimpressed. “It’s not encouraging that Amazon threw that much money at the project before the creative team was put in place,” she says. “It’s putting the cart before the hobbit-sized horse. The whole project faces additional scrutiny because the Peter Jackson films are so damn good. Maybe the team will do a fantastic job. I truly hope so. If they’ve turned it into a bad TV show, millions will be disappointed.”

TV creators must do more than simply be faithful to the source material, says Jane Tranter, head of Bad Wolf Productions, makers of both His Dark Materials and A Discovery of Witches. “You have to remember that, rightly or wrong, TV audiences are much bigger than book audiences. For me, the biggest takeaway from Game of Thrones’ success is the way it highlighted how important world-building is – and how much audiences get from that when you get that world right.”

World-building … A Discovery of Witches. Photograph: Sky

Arguably, the shows that will become hits in world after Game of Thrones will be those least like George RR Martin’s juggernaut. Good Omens has a unique sense of humour and looks set to benefit from Gaiman’s close involvement and some top-notch casting including David Tennant and Michael Sheen, which could prove an inspired pairing.

Gaiman talks about how important it was to stay true not only to his vision but to that of the late Terry Pratchett: “I don’t know if I would have been as obsessive about getting it right if it had been completely mine.” Meanwhile, Adam Whitehead singles out Wheel of Time as a show that could go global. “The fanbase is already there and the TV creators are taking an interesting and slightly idiosyncratic approach.”

Tranter believes that the shows with the best chance of success will be those that offer hope in bleak times. “Post-Game of Thrones,” she says, “the last thing I’d want to do is make an adult male-skewed fantasy with a very full-on attitude towards violence and sex. The great thing about His Dark Materials is that it’s a fantasy that’s very accessible and romantic, that’s open to children and has a positive, optimistic message to send the world. Those are the sort of shows that will resonate right now.”

• Game of Thrones returns to Sky Atlantic and Now TV on 15 April. Good Omens will air on Amazon Prime Video on 31 May and on BBC Two later in the year.