Entertainment

You don’t know Jack (yet)

About 4 a.m. on Dec. 12, 1976, Jack Cassidy, the suave, handsome char acter actor, poured himself a scotch and soda and settled down on the couch in his West Hollywood pent house.

He probably glanced at photographs of himself and his idol, John Barrymore, which hung in profile, facing each other, above his fireplace.

And then, as he always did when he had a drink in his hand, he lit a cigarette.

Some two hours later, fire trucks arrived. The penthouse was in flames.

Firefighters found Cassidy’s charred remains in the front hall. An investigation revealed that he’d fallen asleep while his cigarette smoldered. He crawled to the front door, only to die from lack of oxygen.

He was 49.

Thirty-four years after his terrible death, Cassidy is largely forgotten, although musical-theater buffs cherish his stylish performances on the original cast recordings of “She Loves Me” and “It’s a Bird . . . It’s a Plane . . . It’s Superman!”

With any luck, Cassidy’s son Patrick will soon bring him to life for a new generation of theatergoers. Patrick’s at work on a one-man show about his father, interviewing many of his old Broadway pals, including producer Harold Prince and veteran actor John McMartin.

“He was a dear friend, and one of the wittiest and smartest actors I’ve ever met,” says McMartin. “I always think of him this time of year.”

I’ve been a Cassidy fan since I saw him in a “Columbo” episode playing an arrogant magician who murders a nightclub owner.

Cassidy was such a great “Columbo” villain — elegant, preening, lethal — that he made three guest appearances on the long-running series.

“The whole point was to pit the working-class cop against the rich guy,” says William Link, who, with Richard Levinson, created Columbo. “Jack was perfect. He was so sophisticated, and he had this built-in sneer.”

Cassidy’s public persona, which he modeled on Barrymore, “was completely made up,” Patrick told me when I met him last summer in Dallas, where he appeared in a revival of “Superman” in the role his father originated in 1966.

“My dad was born in Queens but affected this mid-Atlantic accent. The old neighborhood accent only came out when he got mad at us.”

Cassidy was married to Shirley Jones, with whom he had three sons — Patrick; former teen pop star Shaun and designer Ryan. His oldest son, “Partridge Family” star David Cassidy, was from a previous marriage.

Jack Cassidy ran away from Queens at 16 and got a job as a bellhop at the Waldorf-Astoria, where, he later said, he learned from the rich guests what clothes to wear, what wine to order and how much to tip.

“My father only wanted the best, and he firmly believed in living beyond your means,” says Patrick.

Around Broadway, he was famed for his sense of humor.

Critic Martin Gottfried was playing cards with playwright Burt Shevelove one evening when there was a knock at the door. “Who is it?” shouted Shevelove. “Joel Grey,” was the reply. Shevelove opened the door, and there was Cassidy on his knees.

“One on one, Jack was completely without guile,” says McMartin. “But as soon as somebody came over to the table, the smile broke out and the spotlight hit the teeth.”

Says Patrick: “My father could turn his personality on and off like a light switch.”

When it was off, Cassidy struggled with depression and drank heavily. He was frustrated that his movie career never took off, telling McMartin: “They say it’s tough being on top. Well, try being in the middle.”

He didn’t relish the prospect of turning 50, and death was on his mind a few weeks before the fire.

“I remember we were talking about eulogies,” McMartin recalls. “And he asked me that, if he died, would I say something at his memorial. I said I couldn’t because I’d be too upset. He was really offended. I said, ‘If I go first, will you get up there and do anything?’ And he said: ‘Do anything? I intend to sing!’ “

michael.riedel@nypost.com