Autumn of the Jackass - NYTimes.com Martin Schoeller for The New York Times Johnny Knoxville, star of "Jackass Presents: Bad Grandpa." At first glance, the old man in the cardigan and the backpack-toting boy sitting on an outdoor bench in a Los Angeles suburb were an image of harmless innocence: just a drowsy octogenarian being looked after by his fidgety grandson. When the old man leaned back, closed his eyes and appeared to nod off, the cherubic child took out a permanent marker and pulled off its cap. With painstaking precision, the boy proceeded to write the word "fart" in thick capital letters on his grandfather's forehead. Photograph from Paramount/Everett Collection Knoxville during a typical scene from "Jackass: The Movie" (2002). The boy was trying to time his act of human graffiti as unsuspecting pedestrians strode by, hoping to elicit reactions of shock, surprise or disgust. But no one was taking the bait. The would-be victims of this prank hardly noticed the pair as they hurried by, even when the boy cried out for their attention. ("Look what I did to my grandpa!" "Did I spell it right?") One perplexed woman in a sundress started to approach the bench, then asked if she was being filmed. "She really caught on," the boy said as she walked away. "Yeah, that's the problem with shooting in Los Angeles," grumbled the old man, an 86-year-old widower named Irving Zisman. In truth, there is no such person as Irving Zisman. Beneath the layers of makeup, prosthetic applications and fake age spots, he is Johnny Knoxville, the reckless 42-year-old daredevil and ringleader of the MTV reality franchise "Jackass." Zisman is a lascivious if well-meaning character whom Knoxville portrayed in "Jackass" segments, and whom he reprises in the reality-based comedy movie "Jackass Presents: Bad Grandpa." As a matter of fact, there isn't really a Johnny Knoxville, either: he is the alter ego of Philip John Clapp, known to close friends and co-conspirators as P. J., the son of a Tennessee tire salesman and a homemaker, who grew up to become a California transplant with a wife and three children, a Southern twang and a laugh like an asthmatic cartoon dog. He has spent more than 15 years playing Johnny Knoxville, doing everything the role requires. He has been fired out of a cannon, subdued himself with a stun gun and stood blindfolded in a corral while being charged by a yak. He has broken bones, sustained concussions and torn his urethra in a misbegotten attempt at back-flipping a motorcycle. He realizes he has been at this far longer than he or anyone else expected. There are signs that the beatings his body and psyche have taken are starting to catch up with him, though he says he doesn't dwell on them. The person you see, whether cameras are trained on him or not, "that's pretty much me," he says. From the outside, "Jackass" can look like a kind of trap for Knoxville - an outlet he should have outgrown years ago yet one he keeps returning to, perhaps because it's the only thing he knows how to do well. But he sees "Bad Grandpa" as allowing him to reconnect with what was initially fun about "Jackass" all those years ago. "It's just been really liberating that way," he told me from a makeup chair while a team of special-effects artists completed the three-hour process of transforming him into Zisman. "It's just like the early days of "Jackass," when no one knew who I was. I could do anything. Knoxville had arrived at 7 a.m. that morning at the Burbank offices of Dickhouse Entertainment, the production company he shares with Jeff Tremaine, his longtime collaborator and the director of "Bad Grandpa," and the filmmaker Spike Jonze. By 11 a.m., Knoxville, the middle-aged troublemaker, had been replaced by Zisman, a balding, bespectacled old man with a white mustache and wrinkly skin. Soon he was walking the hallways with the spry gait of a man half the character's age. The get-up is convincing enough to fool the dozens of unwitting co-stars of "Bad Grandpa," which Paramount will release on Oct. 25: those well-intentioned civilians who try to help Irving and his grandson (actually a 9-year-old actor named Jackson Nicoll) on their cross-country adventure, and instead get tricked into, say, transporting a dead body from Irving's bed into the trunk of his Lincoln Continental, or watching in horror as he crashes a male stripper's performance during ladies" night at a bar.