Michael Nesmith, the woolcapped singer-songwriter and guitarist who sprang to pop music stardom in the 1960s as a member of the Monkees, then went on to a multifaceted career as a country rock musician, music video pioneer, movie producer and media executive, died Dec. 10 at his home in Carmel Valley, Calif. He was 78. The cause was a heart ailment, said Jason Elzy, the head of communications for Rhino Records, which represents the Monkees. Mr. Nesmith last performed less than a month ago, concluding a Monkees farewell tour in Los Angeles with singer and drummer Micky Dolenz, who is now the band's sole surviving member. Although the Monkees were a made-for-TV band, created by producers Bert Schneider and Bob Rafelson to capitalize on the popularity of the antic Beatles movies "A Hard Day's Night" and"Help!," Mr. Nesmith sought to bring a musical seriousness to the group, which starred on an NBC sitcom for two seasons and became known for chart-topping singles such as "Last Train to Clarksville," "I'm a Believer" and "Daydream Believer." Critics usually panned the band's records, but teenage girls flocked to their concerts: The Monkees' first four albums all reached No. 1, and for a time the "Prefab Four" outsold the Beatles. Mr. Nesmith, a deadpan singer with a Texas drawl, was writing songs and performing at Los Angeles nightclubs when he successfully auditioned to join the Monkees, not quite sure what he was getting into. The group included heartthrob singer Davy Jones and multi-instrumentalist Peter Tork, and went on to play Nesmith songs including "Circle Sky," "The Girl I Knew Somewhere" and "Mary, Mary," first recorded by the Paul Butterfield Blues Band and later covered by Run-DMC. "People think it was amazing that four guys hired for a TV show could actually form a band, but I don't see it that way," Mr. Nesmith told Rolling Stone in 2016. "It's not that amazing when you think of the tenor of the times. You put any four guys in a room in the 1960s and you had a band, all the way from the Grateful Dead to Buffalo Springfield." Premiering on NBC in 1966,"The Monkees" was canceled after two seasons but won an Emmy Award for outstanding comedy. The show was filled with high jinks and mischief-making — the band took to the seas, worked on a ranch and visited a creepy mansion — and featured musical performances in which the Monkees played their hits, or appeared to. Early on, their instruments were unplugged, with session musicians filling in behind the scenes." We were confused, especially me," Mr. Nesmith later said, recalling his disappointment that the Monkees initially lacked control over their music. Songs were overseen by music publisher Don Kirshner and written by leading songwriters including Carole King, Gerry Goffin, Neil Diamond, Neil Sedaka, Tommy Boyce and Bobby Hart. When Mr. Nesmith tried to join the club, offering a song he had written called "Different Drum," he was promptly rejected by the showrunners. They "said to him, 'That's not a Monkees song,' " Dolenz recalled in an interview with Rolling Stone. "Michael said, 'Wait a minute, I am one of the Monkees.' He gave it to Linda Ronstadt, and the rest is history." The song became Ronstadt's first hit when it was recorded in 1967 with the Stone Poneys, reaching No. 13 on the Billboard pop chart. By 1967 the group had taken control of their music, writing and recording most of the songs on their third album, Headquarters." But their popularity plummeted over the next year as constant exposure and shifting musical tastes made the Monkees "a pariah," as Mr. Nesmith put it. They released a critically derided psychedelic film, "Head" (1968), directed by Rafelson and co-written by actor Jack Nicholson, and splintered soon after, with Tork quitting the band and Mr. Nesmith following in his wake. Moving into new musical territory, Mr. Nesmith recorded three country rock albums with the First National Band, which struggled to build a following but scored a Top 40 hit with "Joanne," from its 1970 debut album, Magnetic South." "It's a minor masterpiece of country-rock," wrote AllMusic reviewer Mark Deming, "and while the Eagles may have sold more records, Nesmith yodels a hell of a lot better than any of them." Mr. Nesmith also recorded solo albums including "And the Hits Just Keep on Comin'" (1972), with in-demand pedal steel guitarist Red Rhodes; collaborated with Linda Hargrove to write "I've Never Loved Anyone More," which became a country hit for Lynn Anderson; and founded a record label, Pacific Arts. The company moved into film and video projects after Mr. Ne smith decided to promote his 1976 single "Rio" by creating one of the first modern music videos, a surreal pastiche of classic Hollywood musicals and Disney films that showed him reclining on the beach and dancing at a tropical nightclub. He later included the video in "Elephant Parts" (1981), an hour-long collection of music videos, comedy sketches and parody commercials that earned Mr. Nesmith the first Grammy Award for video of the year. Mr. Nesmith also created the MTV precursor "PopClips," a weekly music-video show that aired on Nickelodeon in the early 1980s, and hosted the short-lived NBC series "Television Parts," a zany, experimental mix of music and comedy. Shifting his focus to Hollywood, he recorded the music and co-wrote the screenplay for "Timerider: The Adventure of Lyle Swann" (1982), a science-fiction film about a dirt-bike racer, and served as the executive producer of the cult classic "Repo Man" (1984), starring Emilio Estevez as a punk rocker recruited to join Harry Dean Stanton's car repos session agency. His projects were funded in part by the vast fortune he inherited from his mother, Bette Nesmith Graham, a secretary who used white tempera paint to invent the correction fluid Liquid Paper, which became an office staple. After her death in 1980, Mr. Nesmith used some of his inheritance to fund nonprofit organizations that she had founded to help women in business and the arts.