Tom Rapp, around 1969. He fronted Pearls Before Swine but quit music in the 1970s and eventually became a civil rights lawyer. (Family Photo/copy shot by Bill O'Leary/The Washington Post)

Tom Rapp, a singer and songwriter with a slight lisp, gentle voice and apocalyptic vision, traits that helped make his band Pearls Before Swine one of the most enduring and eccentric groups of rock music’s late-’60s underground scene, died Feb. 11 at his home in Melbourne, Fla. He was 70.

The cause was cancer, said his son, David Rapp.

A self-taught musician who learned the guitar from Joan Baez records and infused his lyrics with allusions to English poets and Greek myths, Mr. Rapp inspired acts including Elton John and the experimental pop collective This Mortal Coil. Still, commercial success eluded him — he said he earned no more than $200 throughout his career — and he quit music in 1976 after less than a decade of full-time performing.

Mr. Rapp went on to cut his shoulder-length red hair, trim his beard and become a civil rights lawyer in Philadelphia, practicing a brand of law that he described as an extension of his politically provocative music — songs that envisioned a ghostly march on Washington by children killed in Vietnam or examined suffering from an oblique, often mystical or sci-fi-tinted angle.

On one track, “Rocket Man,” Mr. Rapp sang of an absent father who “often went to Jupiter or Mercury, to Venus or to Mars” but eventually disappeared altogether: “One day they told us the sun had flared and taken him inside.”

A song of the same name became a hit for John and lyricist Bernie Taupin, who once told Billboard magazine that he borrowed its subject matter not from David Bowie’s “Space Oddity” but from “Tom Rapp and a band called Pearls Before Swine.”

05/07/98 PHOTOG: Bill O'Leary LOCATION: Philadelphia, PA and Haddonfield, NJ CAPTION: Tom Rapp fronted a folk-rock band in the late sixties and early seventies. As 'Pearls Before Swine', he made nine albums, but never broke through to major success. He chucked music in the late seventies, got a law degree and is now practicing law in Philadelphia. Lately, his music has been gaining popularity. Pictured, Tom Rapp, after work, relaxes with his dog 'Harry'. (Bill O'Leary/The Washington Post)

Mr. Rapp’s musical career got off to a promising start in 1967, when his band’s debut record, “One Nation Underground,” sold more than 200,000 copies — an unlikely success for an album that featured a section of Hieronymus Bosch’s painting “Garden of Earthly Delights” as cover art.

The record mixed rock, folk, blues and classical music in a style that Mr. Rapp sometimes described as “transcendental rock,” and it featured nontraditional instruments such as the celesta, finger cymbals, autoharp and the Nepalese sarangi. Recorded in four days, the album rose to prominence on the strength of songs such as “Another Time,” inspired by Mr. Rapp’s near-fatal car crash in an Austin-Healey Sprite, and “(Oh Dear) Miss Morse,” which rhymed the name of media theorist Marshall McLuhan with “your ruin” and spelled a four-letter word in Morse code.

“I tried L-O-V-E first,” Mr. Rapp told The Washington Post in 1998, “and the cadence was all wrong. Then I tried that, and you know, it was like God wanted that word in that song. It got [rock-radio DJ] Murray the K in trouble.”

Mr. Rapp went on to tour with Buddy Guy, Gordon Lightfoot, Chuck Berry and Bob Dylan, a fellow Midwesterner whom he had bested, years earlier, at a local talent show in Minnesota. He was invited to appear at Woodstock in 1969 but turned down the invitation, preferring to remain in the Netherlands, where he was writing music at the time.

Mr. Rapp’s second record with Pearls Before Swine, “Balaklava” (1968) — named for the location of the famed Charge of the Light Brigade during the Crimean War, which he described as “the last time that war was glorious” — was a critically acclaimed work of ­anti-Vietnam protest music.

He later released four more albums under the Pearls name and three solo records before retiring from music, frustrated by the industry’s business practices. He said Bernard Stollman, the founder of his first record label, ESP-Disk, never paid him; Mr. Rapp once speculated that this was because Stollman “was abducted by aliens, and when he was probed it erased his memory of where all the money was.”

Later, Mr. Rapp told The Post, he was swindled by a producer who netted more than $100,000 in royalties and took ownership of his music. By then, he was broke, living at times on nothing but oatmeal. When he stopped performing, he sold popcorn at a movie theater, earning $1.35 an hour.

“I knew at the end of the week, every single week, I would get $85,” he told The Post. “I was insane with joy!”

Thomas Dale Rapp was born in Bottineau, N.D., on March 8, 1947. Both his parents were schoolteachers, and his father was a heavy drinker who — like the astronaut of “Rocket Man” — sometimes disappeared for extended periods.

Mr. Rapp lived in Minnesota and Pennsylvania before graduating from high school in Melbourne, where he and his friends named their band Pearls Before Swine after a line from Jesus’ Sermon on the Mount.

He received a bachelor’s degree from Brandeis University in 1981 and graduated from law school at the University of Pennsylvania three years later, focusing on discrimination law in a legal career that eventually took him to Florida.

His marriages to Elisabeth Joosten and Susan Hein ended in divorce. Survivors include his wife of 22 years, Lynn Madison of Melbourne; a son from his first marriage, David Rapp of Brooklyn; two sisters; and a granddaughter.

Mr. Rapp eventually returned to music, performing in 1997 with his son’s band, Shy Camp, at the Terrastock music festival in Providence, R.I. He released a solo album, “A Journal of the Plague Year,” two years later, recording with the psychedelic-folk duo Damon & Naomi and the Bevis Frond, a British rock group.

Mr. Rapp’s debut album with Pearls Before Swine was reissued in October by the record label Drag City. When The Post profiled Mr. Rapp in 1998, the singer said he didn’t have a copy of the original album. Out of circulation and rare at the time, he said it cost too much — $30.

“I didn’t get that much to make the album,” he said.