Gods die when you stop praying to them. Celebrities do reality shows when you stop buying their records. Movie stars write cookbooks when you stop seeing their films. It’s like a law of life.  Just ask Ozzy Osborne.

So when you see Liam Neeson’s hangdog look in Wrath of the Titans, opening on Friday, it’s because he’s playing the god of all gods Zeus, and he remembers a time before fickle humanity moved on and left him in history’s trash bin.

It’s hard to picture Neeson in a second fiddle role and even more surprising to discover it’s a demotion that he’s sharing alongside veteran Ralph Fiennes, his Oscar nominee nemesis from Schindler’s List, who now plays his Olympian brother Hades, lord of the underworld.

The superstar Irish and British actors and their spirited turns are the best things in Wrath of the Titans and ironically enough, for a pair of Greek gods at war, they still somehow manage to inject the film with a rich vein of touching humanity in the middle of all the spectacular set pieces and battles.

Neeson, 59, who hails from Ballymena in Co. Antrim, has retained all of his northern stoicism, which is a distinct advantage when it comes to his latest deity role. But dangerously weakened by humanity’s lack of devotion, Neeson plays a god in the process of losing his immortality – and his mojo.

The plot of Wrath of the Titans kicks in when we discover that there are consequences for this dramatic power changeover. The most horrifying one is that once Zeus begins to lose his heavenly powers, he also begins to lose his hold over a host of imprisoned underworld nasties just waiting for the chance to get even with him. Taken prisoner by Hades, he’s being drained of his power and the world is collapsing.

It all falls to demigod Perseus (Australian actor Sam Worthington) to prevent hell from opening on Earth, so he must embark on a great journey into the Underworld to free his father Zeus and restore the peace. But how on earth do you prepare for such role?

“My favorite scenes were with Sam in the beginning when I ask for his help,” Neeson reveals to the Irish Voice. "I treat these characters as un-godlike as possible otherwise you could never play them. You’d be too intimidated."

For Neeson, preparing to play the king of Olympus really isn't any different from Oscar Schindler or Michael Collins. You just find the story and you tell it.

“Westerns are for me like Greek mythologies," Neeson says. "It’s all the same story, you know? In my twenties in Ireland I started reading Greek mythology. And I read them in preparation for The Phantom Menace,” he says, adding a rare smile to suggest he’s joking.

But even if he wasn’t joking Neeson has reason to be proud of his Star Wars prequel. Although it was almost universally loathed by critics and fans alike it is still, adjusted for inflation, the most successful film of all time.

Blockbusters have added a few bells and whistles since director George Lucas unveiled the first prequel to the Star Wars trilogy in 1999. For one thing 3D is suddenly back in vogue as a crowd puller, and in Wrath of the Titans it's one of the film's major selling points. But it also makes an actor’s job harder, having to act with green screens and stick men where terrifying monsters should be.

“I’m from the old school, from the first Star Wars, where the actors used tennis balls for reference,” says Neeson archly. “I’m quite fond of those. On Titans we used lots of bits of colored tape as well. You have to act sometimes with bits of tape and that’s okay.”

Having starred in Avatar, the most expensive sci-fi flick ever made, Worthington knows all about the high tech demands made of actors on set and they don't bother him. All he cares about is the story.

“There wasn’t a myth to base Wrath of the Titans. In the original myth, the one we covered in Clash of the Titans, Perseus becomes a king and has many children and lives happily ever after,” Worthington says.

“So the writers and actors were on all new ground with this retread of old gods in new capers. What would be a fun adventure for Perseus to go on next? What would really challenge him? These were the questions the writers and the film ask.”

The movie they created ends up being all about the dysfunctional relationships between fathers and sons and in many ways Perseus is the ultimate example of a man overshadowed by his more accomplished dad. His journey is all about how he steps out of his fathers shadow.

“The director Jonathan Liebesman always brought it down to the story,” explains Neeson. “We knew that there were going to be 280 explosions in this scene but he brought it down to where our characters were in the tale at that moment.”

It was the chance to explore the relationship between father and son that drew Neeson back to the sequel, he says.

"I just wanted more interaction with my son and my brothers in this one, which I think this script certainly provided. It touches on those dynamics of how Hades became separated from his brother, and on the jealousies that drove them apart. That’s all touched on,” he says.

“The father son relationship is one that we can all relate to too, you know? In Wrath of the Titans the dysfunctional family just happen to be gods.

“Liam's right.” agrees Worthington. “When monsters attack Perseus looks for his son, not for action. The film is about two estranged brothers coming together to knock out their own father. So it’s a family story in the midst of a spectacular blockbuster. If we lose sight of that then we lose the film.”

What’s powerful about Greek mythology, and the reason it endures, is that it has so much to say about human nature and our everyday experiences. What’s happening involves gods and mortals, but it’s also human scale and about all the things we care about: love, family, justice, war and peace and of course romance.

People who have studied Greek myth often come to know its principal players better than they know their own families. They're the ones most likely to grouse at the liberties taken by the new storyline. Worthington has a message for them.

“F*** them, I don’t care. We can utilize and mine this great field of characters and creatures and take them on new journeys,” he says.

“For me as an actor that’s probably the most exciting thing about the new film. We can create our own mythologies.”

He has a point. After all, the Romans did it to the Greeks, changing their mythologies by changing the names of all the principal players. Christianity did the same later on too, a fact that is perhaps less well known.

A standout scene in the new film involves a cameo star turn from the uniformly excellent British actor Bill Nighy, who plays fallen god Hephaestus.

Performing with a Monty Python style north of England accent, he seems to belong to a completely different universe and a different film, which at this point comes as a relief from all the father and son navel gazing that has been going on.

For Neeson, the whole experience was a romp and becoming Zeus was as easy as finding the right wig.

“I had a great head of hair, that helped a lot actually. And I thought it was important not to show power. If you try to show it you immediately weaken your character. Zeus doesn’t have to prove he's powerful. He just is.”