RAB C Nesbitt writer Ian Pattison had no sooner written the hit stage play I, Tommy when he came up with an idea for another play featuring a larger-than-life character.

Just like Tommy Sheridan, the man would be clever and charismatic - but flawed.

Ian had turned his attention to cult Glasgow-born psychiatrist RD Laing, a man who shook the foundations of the medical world with his theories on how to treat mental illness.

RD Laing's work redefined the relationship between patient and doctor.

He believed the family to be a potentially destructive force on the individual and once said 'We are effectively destroying ourselves with violence masquerading as love.'

Yet, Ronnie Laing's own family life was chaotic.

Now Ian's play Divided, which runs at Oran Mor this week, focuses on a pivotal moment in the life of Laing, a man who took LSD, hung out with rock stars and had 10 children.

But who to play RD Laing, who died 24 years ago?

Billy Mack seemed perfect casting. Growing up in Bridgeton, like Laing, he has gone on to enjoy some incredible life experience.

"Yes, that's certainly the case," says Billy.

"When I was a teenager I was a bit of a joker and not very academic at school so I went to drama college.

"This was 30 years ago. I was in my second year there when my father died, and I dropped out.

"I had to go out and get a job to support the family.

"The thing is, my father was an incredible character, just in his early forties when he died, and there isn't any way I'd have dropped out if he'd been alive.

"He was the type - he was in the RAF - who reckoned if you took on a job you had to see it through."

Billy reckoned he had to become the breadwinner.

And so he worked on fishing boats, became a labourer, took off to London, then eventually landed work on the North Sea oil rigs as a roustabout.

"It was a hard life," he explains of the off-shore adventure.

"Those guys have a it tough. What you do is everything you can to keep the oil pumping, changing tools, machinery. And in many ways it was satisfying. You made some great friendships.

But there was a price to pay for the high wages.

"I saw so many relationships disintegrate," he recalls. "So many marriages just couldn't cope with the strain of people being apart for so long."

Billy's relationship also crumbled. His partner left him. And he had to re-evaluate his life.

Thanks to encourgement from friends on the rigs, he determined he should have been an actor after all.

He did one last stint on the rigs, saved some money and paid his way back into drama college. A decade to the day, he returned to Glasgow's RSAMD.

"It was great going back," he says.

"I had lived something of a life, and it meant I had more to offer as a actor.

"The first time round at drama school we were exploring themes such as love and loss, but I didn't know what love was.

"I was a wee boy. And I didn't know about loss either, until my father died.

"What was also important was my attitude had changed. I was now desperate to learn. I was focused."

Billy left drama school and has gone on to work successfully with a series of theatre companies, such as the Citizens.

Now, he's revelling in the chance to play such a fascinating character.

"I've fallen on my feet with this man," he says of RD Laing. "Not only was he brilliant, he was an entertainer.

"And he was a rebel and slightly off-the-wall. But he was also a working class hero. And conflicted.

"This play looks at a man who, in his career, focused on the dynamics of the family, yet as a father he was less than perfect."

Billy adds; "I've been looking at film of him on YouTube, and that's given me a few pointers."

Billy Mack certainly has the energy required to play such a dynamic man.

"I hope so. I can understand, to a degree, how RD Laing backed away from responsibility, yet with my own two girls I just want to see them grow up and experience their adventures.

"I don't know how Ronnie Laing didn't see things that way."

Billy's two girls, aged 12 and 15, are causing the actor a little consternation at the moment.

"They've been helping me learn my lines, reading in the female parts for me at home, and they've been fantastic," he enthuses.

"But the thing is, they're both saying they'd like to go into acting."

He adds, with a wry smile; "Here's me thinking they'd be lawyers or whatever and keep me comfy in my old age.

"But it doesn't look as though it's going to happen."

l Divided, Oran Mor, until Saturday. 1pm. Oran Mor, Byres Road, 08444 771 000. £8-£12.50.