Kary Mullis, who shared a Nobel Prize in chemistry for devising a technique vital in DNA research and technology and who appeared to be one of the most unconventional winners of the award, died Aug. 7 in Newport Beach, Calif. He was 74.

The cause was pneumonia, said his wife, Nancy Cosgrove Mullis.

The technique for which Dr. Mullis shared the Nobel in 1993 was known as polymerase chain reaction, called PCR for short, and it enabled scientists to make millions or billions of copies of a single tiny segment of the DNA molecule.

Often described as a major milestone of 20th-century biochemistry and molecular biology, the PCR technique opened the way for a wide variety of studies and applications of DNA, the celebrated molecule that lies at the foundations of life.

In only one of many applications, PCR was used by evolutionary biologists to study the minuscule quantities of DNA discovered in the fossils of ancient species. The possibilities suggested by this technique inspired the creation of dinosaurs in such fictional films as “Jurassic Park” (1993).

Widely acknowledged for its significance, PCR not only rewarded Dr. Mullis with the most coveted prize in science, but it also provided a platform that he bestrode with relish for his free-spirited, often quirky ideas and lifestyle.

A writer, a surfer and a restless, questing personality who once turned from science to manage a bakery, Dr. Mullis published a memoir titled “Dancing Naked in the Mind Field” (1998).

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It embellished his reputation for happily ignoring the normal strictures, cautions and conventions that were observed by so many others in science and scholarship, particularly those at the exalted levels of Nobel winners.

It is true that, despite the title of his memoir, he did not appear unclothed on its dust jacket. But few if any other Nobel winners published anything showing themselves bare-chested with a surfboard tucked under an arm.

Among the exploits and adventures for which he was known was experimentation with the hallucinogenic drug LSD. It was this that reportedly made the defense team representing O.J. Simpson, the former football standout acquitted in 1995 of the killing of his ex-wife and her friend, decide against calling him as an expert witness in the case.

Although the trial has often been depicted as a courtroom circus, he once told an interviewer that it was feared that his appearance might have only made the proceedings seem more of one.

A 1966 chemistry graduate of Georgia Tech who held a 1973 PhD from the University of California at Berkeley, he appeared in many ways to be one of the most prominent representatives in the scientific community of the mind-set of the counterculture that was centered in California in the 1960s.

In his Nobel lecture, he told the assembled dignitaries that “six years in the biochemistry department didn’t change my mind about DNA, but six years of Berkeley changed my mind about almost everything else.”

A fount of ideas sufficiently offbeat to make fellow scientists frown, he seemed skeptical of much conventional wisdom, including theories that were widely held in science. Doubts about whether climate change was man-made or whether HIV caused AIDS helped make an outlier in the scientific establishment.

In addition, his apparent enthusiasm for astrology and seeming fondness for such ideas as astral projection and the possibility of abduction by aliens also led his scientific peers to look at him askance.

Such flouting of scientific norms led one colleague to reportedly characterize him as an untamed genius.

Kary Banks Mullis was born Dec. 28, 1944, in Lenoir, N.C., and started life near the North Carolina Blue Ridge, where his forebears had roots. When he was about 5, the family moved to Columbia, S.C.

In high school there, he demonstrated an interest in science and scientific exploration by launching rockets, powered by homemade chemical fuel. In his Nobel lecture, he described with great gusto his early rocket trials.

“In one of our last experiments before we became so interested in the maturing young women around us that we would not think deeply about rocket fuels for another 10 years, we blasted a frog a mile into the air and got him back alive.

“In another, we inadvertently frightened an airline pilot, who was preparing to land a DC-3 at Columbia airport. Our mistake.”

In the same lecture, he appeared scornful on the rules and restrictions of the current era that might deter such after-hours experimentation in the school laboratory.

“We spent many an afternoon there tinkering. No one got hurt and no lawsuits resulted. They wouldn’t let us in there now. Today, we would be thought of as a menace to society.”

A biographical sketch describes his family and his boyhood days in detail. But after that, he wrote, in what seemed a clear reminder of his whimsy, “The rest of my life has passed quite suddenly. Around ten or twelve I fell into the inevitable logarithms of time. It seems to go faster and faster. I wonder now why we have to have Christmas so often.”

After receiving a doctorate in biochemistry from Berkeley, Dr. Mullis did research at other universities before joining Cetus Corp., then a San Francisco Bay area biotechnology firm, where he said he “was working when I invented PCR.”

He later became the chief of molecular biology for another corporation, Xytronyx Inc., in San Diego. Subsequently, he has been described as freelancing as a consultant.

His marriages to Richards Haley, Gail Hubbell and Cynthia Gibson ended in divorce. Besides his wife, to whom he was married for 22 years, survivors include a daughter from his first marriage, Louise Olsen; two sons from his third marriage, Christopher Mullis and Jeremy Mullis; two brothers; and two grandchildren.