Chevy Chase has made us laugh since his first routines on "Saturday Night Live" in 1975, but behind the clownish façade are horrific memories of a childhood of beatings and psychological torture by a mentally ill mom and twisted stepdad.

"I lived in fear all the time - deathly fear," Chase says in a new authorized biography, "I'm Chevy Chase . . . And You're Not," by Rena Fruchter, out next month from Virgin Books. It reveals that Chase's concert-pianist mother, Cathalene, was a "very unhappy woman" who suffered from depression and panic attacks that could set her off at a moment's notice. They had her locking young Chevy in a closet for hours at a time and waking him up in the middle of the night to slap him "continually and hard, across the face," Chase tells the author. "I don't remember what it was for, or what I had done."

One of her other brutal punishments was to whip Chase over a period of days. "She would say to me, 'Ten lashes on the backs of your legs every day for a week at 5 p.m.' How can you hold on to that kind of anger against your kid?" Chase relates to Fruchter. "I knew I was a 'bad boy,' but I didn't know that everybody wasn't punished the same way I was."

Chase's younger half-brother, John, tells the author: "My mother, at her worst, was like an unleashed animal. It was at her hands, in her feral states, that Chevy suffered the darkest of his secret torments."

Chase was also traumatized by his mom's second husband, John Cederquist, who heaped on him "emotional and physical abuse that sometimes bordered on torture," Fruchter writes.

The comic, who starred in such flicks as "Caddyshack" and "National Lampoon's Vacation," is 63 now, and his tormentors are dead. But, he tells Fruchter, "I always turn to it in my mind . . . I'll never forgive them. At their graves I didn't. It was too hard for me. You would think a grown man could shake it off, as the coffin was being lowered, to say, 'I forgive you.' I don't forgive."