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The first half of “Supernatural’s” debut season gave few indications of what the show would become.

Back in 2005, as is the case now, there were monsters, ghouls and demons on the prowl. Two brothers, Sam and Dean Winchester (Jared Padalecki and Jensen Ackles), would go from city to city in their 1967 Impala and hunt these otherworldly critters down, frequently quipping along the way.

But creator Eric Kripke is well aware that “Supernatural,” which returns for its fifth season at 8 p.m. Thursday on WGN-Ch. 9, has evolved far beyond the idea he pitched several years ago.

Season 5 depicts the brothers trying to stop the apocalypse, dealing with the arrival of Lucifer (Mark Pellegrino) and other significant events. Yet the focus of this solid, compelling and funny (yes, funny!) show remains admirably clear: “Supernatural” is less about monsters and more about familial bonds and how they somehow survive self-doubt and radical tests of loyalty.

When the show began, Sam and Dean were merely “an engine to get us in and out of different horror movies every week,” Kripke said in an interview at San Diego Comic-Con in July.

Then Kripke had an epiphany: Padalecki and Ackles’ subtle skills and palpable chemistry could anchor a much more emotionally compelling story about two young men who lost their parents and sometimes come close to losing faith in themselves and each other.

“To me, the story is about, ‘Can the strength of family overcome destiny and fate, and can family save the world?'” Kripke said. “[My worldview] is that the only thing that matters is family and personal connection; that’s the only thing that gives life meaning.”

The show’s fourth season upped the stakes in several ways: When he thought his brother was dead, Sam became addicted to demon blood and experimented with dangerous powers. Dean, who’d been sent to hell to fulfill a contract, was pulled out by an angel, but only after going through terrifying experiences, some of which left him guilt-ridden.

Kripke said the show had always planned to bring in ever more powerful demons, including Lucifer, but he hadn’t thought about adding angels until Season 3 was over.

“We [always] wanted this ‘Lord of the Rings’ scope, but we could never have it because we couldn’t afford these massive battles,” Kripke said. “But … now you can have these two massive armies of demons and angels — they can mesh and clash in a way that’s really satisfying, and [you can have the giant clashes] just off-camera.

“We slap our forehead against our hands, and say, ‘Why didn’t we think of it sooner?'” he said. “Look at ‘Star Wars’ for a moment. You have this massive empire, and you have this massive rebellion. But the story is about one farm boy, a princess and a pirate.”

To read the transcript of the full interview with Kripke, go to bit.ly/xrP8d.