Robert A. Moog, 71, who invented the Moog electronic synthesizer, a keyboard that became central to rock and electronica bands of the 1960s and 1970s, died of a brain tumor Aug. 21 at his home in Asheville, N.C.

When Dr. Moog's synthesizer appeared in 1964, it resembled a World War II-era operator switchboard. Modified slightly, it burst to prominence on Walter Carlos's Grammy Award-winning recording "Switched-On Bach" (1968), which took many of the classical composer's works and gave them a bubbly, electronic reworking.

The Moog became one of the most widely used novelty instruments of the period, appearing in commercials (for Pepsi); in films ("A Clockwork Orange," performed by Carlos); and on pop recordings (from the Beatles' "Here Comes the Sun" to Donna Summer's disco hit "I Feel Love").

The Byrds, the Rolling Stones, Stevie Wonder and Pink Floyd also experimented with Moogs, as did avant-garde pianist Paul Bley, who featured the Moog and a topless singer in a 1969 concert. A flurry of albums were produced with such titles as "Moog Espana," "Moog Power" and "Music to Moog By," less and less to Dr. Moog's satisfaction.

"Sure, I like the idea of my name becoming a generic term for the synthesizer," he told the New York Times in 1969. "But I don't like the fact that cruddy records are being put out with my name attached."

He added: "There are maybe 25 people in the world who have the necessary competence in both physics and music" to play the Moog satisfactorily.

In 2002, he belatedly received a Grammy recognizing his technical achievements.

Robert Arthur Moog -- his Dutch-German surname rhymes with "rogue" -- was born in New York City on May 23, 1934. He bristled at the hours of piano lessons he was forced to take growing up in Queens but had fun in the workroom of his father, a Consolidated Edison electronics engineer.

After reading a magazine article about the theremin, an eerie-sounding electronic instrument, he assembled one himself, less as a musical challenge than as a mechanical one. Because of its wide range of octaves, the theremin can sound like a human voice, a stringed instrument or a deranged animal, and it is manipulated by moving one's hands between two antennas.

What intrigued him, he once told London's Guardian, was "the idea that you could wave your hands in the air and actually change something."

In 1954, he began to sell his theremins. Among his customers was the sound pioneer Raymond Scott, a studio bandleader and tinkerer extraordinaire who had cut off the theremin's pitch antennas and reassembled the device with wires in back of a keyboard.

This "Clavivox," Dr. Moog once wrote, "was not a theremin anymore -- Raymond quickly realized there were more elegant ways of controlling an electronic circuit."

He added: "Raymond had everything adjusted so that, sure enough, when you played the keyboard you got the notes of the scale. But the really neat thing, as he pointed out, was that now you could glide from note to note -- you could play expressively -- you didn't have to play discrete notes."

This had a lasting impact on Dr. Moog as he completed his schooling: a bachelor's degree in physics from Queens College, a master's degree in electrical engineering from Columbia University and a doctorate in engineering physics from Cornell University, where he was famously late for his PhD defense.

According to the book "Analog Days" (2002), a history of the Moog synthesizer, Dr. Moog walked into an elevator on his way to the PhD defense and immediately became obsessed with the resonant frequency of the elevator: "Bob started jumping up and down on the floor [and] somewhere between the fourth and fifth floors he hit the right frequency. The elevator suddenly started bouncing alarmingly in time with his jumps and ground to a halt. Four hours later he was rescued."

At Cornell in the early 1960s, he met composer Herb Deutsch, a key advocate of electronic sounds. With inspiration from Deutsch, he created the analog synthesizer and promoted it successfully at an audio engineering society convention in the fall of 1964. A novel feature of his instrument was its attack-decay-sustain-release envelopes, which control the way notes swell and fade.

Dr. Moog called himself "a toolmaker with musicians for customers" and sought their advice on how he could improve his synthesizer. He installed a filter at the suggestion of electronic keyboardist Walter Carlos (later Wendy Carlos after a sex-change operation). After Carlos's "Switched-On Bach" album, Dr. Moog reaped a fortune for several years through sales at his workshop, based in Trumansburg, N.Y.

He developed a more portable instrument, the Minimoog, that also sold well, but competition, a recession and his admittedly poor marketing skills led him to sell his business, along with the rights to his Moog synthesizer name, in the early 1970s. After years of struggle, he regained the name in 2002.

By that time, he was long ensconced in the Blue Ridge Mountains of western North Carolina, where he ran a mail-order and retail electronics business now called Moog Music.

He cut a bizarre figure, with an ever-present pocket protector, a wave of white hair and a cautious but not always politic way with words. He drove a 1980 Toyota Tercel with a butterfly, snail and goldfish painted on the side and for years had a bumper sticker that read: "Theremin Players Do It With High Frequency!"

His marriage to Shirleigh Moog ended in divorce.

Survivors include his wife of nine years, Ileana Grams of Asheville; four children from his first marriage; a stepdaughter; and five grandchildren.

Robert A. Moog plays his electronic synthesizer with the Going Baroque band at a church in Asheville, N.C., in 1980. In 2002, nearly 40 years after the instrument first appeared, he received a Grammy for his technical achievements.