It’s probably a good thing that Robert Johnson has three graves outside this Mississippi Delta town. If the devil comes back to claim his share of the royalties, the confusion should give the long-dead bluesman a head start.

On the other hand, the people he really might need to shake are the interpreters, mythologizers, agents and lawyers.

The legendary bluesman, possibly the most influential of the Delta acoustic school, would have turned 100 Sunday. Johnson’s birthday is being celebrated here with a four-day festival of music, art, talk, T-shirts and posters. Leflore County’s 825 hotel rooms are almost all booked. German public radio is making an hour-long special. One of the headliners is Johnson’s grandson Steven, who will play music Saturday night in the town park and preach a sermon at a country church Sunday afternoon.

Such Robert Johnson songs as “Sweet Home Chicago,” “Dust My Broom” and “Cross Road Blues” are part of the repertoire of nearly every musician seeking the roots of this uniquely American musical genre. They’re on records by Cream, Led Zeppelin, the Rolling Stones and many other bands. There are 30 records with at least one Johnson song on them that have sold more than a million copies.

“His songs have made millions of dollars for dozens of people,” said Stephen LaVere, a Greenwood resident and one of the people responsible for turning the bluesman, who died at age 27, into a postmortem commercial success.

“We wonder why Robert was so important today when there were lots of other cats who sold tons more records and who had lots more sway among other artists in their lifetime,” said Scott Ainslie, a 58-year-old singer and musicologist from Vermont who’s here this weekend and has done more than anyone to deconstruct Johnson’s performance technique.

The answer, according to Ainslie, lies in Johnson’s ability to recapitulate piano stylings on the guitar, his eagerness to incorporate what he learned from live musicians and from records, and his strategic appreciation of the 78 rpm disc’s demand for art lasting just three minutes.

Whatever the explanation, the rediscovery of Johnson in the 1960s, when some of his 29 recorded songs were released in LP form, was a revelation.

“Robert was like a gateway drug to the world of the blues for young rock-and-rollers and blues fans like me,” Ainslie said.

Born in Hazlehurst, Miss., 120 miles south of Greenwood, Johnson spent most of his life in the Delta, which is the oval flood plain of the Mississippi and Yazoo rivers running from Memphis to Vicksburg, Miss. He was a “walking musician,” a professional who, unlike many of the blues’ founding fathers, used his talent to escape a life of farmwork. He performed in countless juke joints in Mississippi and Arkansas, traveled as far as St. Louis and Brooklyn, N.Y., to play, and recorded 29 songs in two recording sessions, one in San Antonio in 1936 and the second in Dallas in 1937.

His travels and playing came to an untimely end, however, when he died Aug. 16, 1938, outside Greenwood. The cause was reportedly whiskey poisoned by a juke-joint owner, whose wife Johnson was romancing. He lingered two to six weeks before succumbing to pneumonia or died raving in a few days — accounts differ. And was buried someplace.

His high-pitched voice and haunting, inscrutable lyrics captivated listeners when a collection of some of his songs was released in 1961 as the album “King of the Delta Blues Singers.” Musicians were impressed by his virtuoso guitar work. After hearing a song in which there was a rhythm-bearing bass line and intricate melody-making, Keith Richards famously remarked, “Who’s the other guy playing with him?

Soon after came the story that, along with the mysterious circumstances of Johnson’s death, the man’s legend was clinched.

Johnson had reportedly gone to a crossroads at midnight and sold his soul to the devil in exchange for the ability to play guitar like no one else. The reason for the story was Johnson’s spectacular improvement after he left his home in the north Delta town of Robinsonville about 1930 and returned some time later able to outplay his mentor, Son House. But it might be that in the recollections of old men, which constitute most of the source material for histories of the blues, the Delta Dr. Faustus was actually another bluesman, Tommy Johnson, no kin.

This legend, Robert Johnson’s itinerancy, the lyrics of the songs and his death gave rise to his reputation as a lonely, unmoored, sexually alluring, vision-seeing and slightly dangerous genius. At least that’s what many writers of biographical sketches and liner notes made of him. More recent research and the full accounts of people who once played with him describe Johnson as, among other things, an astute, hardworking musician who was willing to teach people some of his licks.

“He was ambitious, and he was operating in a commercial culture. He wanted a piece of it, and he got one,” said Ainslie, who opened the first of two nights of music in Greenwood’s Whittington Park with his versions of Johnson tunes.

There has been a more modern — but many believe truly hellish — coda to the story, as Johnson’s descendants and their agents have battled over rights to his music and image.

While functionally in the public domain for decades after Johnson’s death, the songs were copyrighted in 1991 by LaVere, a music publisher and blues historian. But he had an arrangement to share future profits with one of Johnson’s half sisters, Carrie H. Thompson. In 2000, Johnson’s born-out-of-wedlock son, Claud, was declared Johnson’s legal heir. Legal proceedings of Dickensian complexity have consumed much of the past two decades. The rights are now held by the New York-based Music Publishing Co. of America, with Claud Johnson, 79, owning a share.

LaVere has the rights to the two verified images of Johnson, which are being litigated. One shows him grinning in fedora and pinstripes, strumming a guitar. The other, a photo-booth self-portrait, shows him holding his guitar, with an unlighted cigarette dangling from his mouth. (Taking liberties with history, the U.S. Postal Service removed the cigarette on the stamp of Johnson issued in 1994.)

Perhaps the only two people alive with recollections of Johnson weren’t able to make it here this weekend. David “Honeyboy” Edwards, a guitarist who lived in Greenwood, sometimes traveled with him and saw him after his fateful gig at the Three Forks juke joint, was scheduled to play Saturday night. But he is 95 and ill and couldn’t make it. Neither could Claud Johnson, a retired gravel-truck driver who ran a barbecue restaurant with his wife in Crystal Springs, Miss.

He recalls seeing his father only twice. He was about 7 years old and living with his maternal grandparents. His father paid two visits a few months apart, looking for Claud’s mother, whom Claud says Johnson wanted to marry. Claud’s grandfather, a preacher, made him stand in the yard.

“I stood there in the doorway,” Claud Johnson said about the second visit in a telephone interview last week. “He was well dressed. He had on some nice trousers, a white shirt and a hat — a well-dressed guy. They talked to him for about 15 minutes. I never did see him again after that.”

Other visits are being paid this weekend.

Parked on the gravel outside Little Zion Missionary Baptist Church just north of Greenwood on Thursday afternoon was a heavily laden van with Ontario license plates. Clustered around a gravestone marking the best-guess resting place of Johnson were John and Sharon Way-Brackenbury and their three children. They were wandering north on the blues trail after spending 10 days in New Orleans working on Habitat for Humanity projects.

Under the shade of a giant pecan tree, Keiran, 16, played “Sweet Home Chicago” on an acoustic guitar while his parents and sisters, Bridget, 14, and Claya, 9, sang. Afterward, one of the children scratched a small hole in the wet ground in front of the stone and buried a guitar pick. Claya tamped the dirt down with her foot.

“Be gentle,” her father said. “Remember, it’s sacred ground.”