Figuring out the best way to portray Walter Bishop — the brilliant, eccentric scientist at the heart of “Fringe” — would be a tricky proposition for most actors. But for Australian-born theater vet John Noble, inspiration came easily, thanks to a former flatmate.

“I used to share a house with a man who was indeed a mad scientist,” Noble says with a laugh. “I adored him, but he was deliciously controversial, always getting into trouble with the authorities.”

Walter is on the other side of the law, having been released from an insane asylum after two decades to help a tenacious FBI agent solve a string of freaky cases that have ties to his own past experiments. As compelling as those cases may be, though, it’s Noble’s deft portrayal of his character’s battle with mental illness and attempts to rebuild the fractured relationship with his con-man son that grounds the Fox drama.

“It doesn’t matter how fun and tantalizing the cases are,” says the actor, who works with an on-set dialect coach to perfect Walter’s Boston accent, “if you can’t invest in the characters.

“I didn’t want to do a caricature of a man with mental illness,” Noble continues. “I decided not to make the cheap choices. Walter is on the road to redemption, and it’s a beautiful thing to be able to grow that over a long period of time on a series. That’s something I’ve never had the opportunity to do before.”

The actor, who appeared as Denethor in the “Lord of the Rings” franchise, is clearly relishing the profile boost that has come from his first regular gig in the States.

“People are always saying, ‘We love the show, we love Walter,'” Noble marvels. “It’s a beautiful journey, and I’m just excited to be along for the ride.

What do you like most about your character?

“I admire the pure part of his mind and that, fundamentally, he’s a kind man. It must be terribly hard for someone of his intelligence and abilities to actually relate to anyone, but he still tries in his own Walter way.”