When Magic Slim thundered at the microphone — his voice rough and ragged, his guitar riffs tough and punchy — listeners heard classic Chicago blues as it was conceived in the 1950s.

Not nostalgic or dated, but simply unconcerned with latter-day musical fashion or commercial considerations.

That approach, which Magic Slim clung to throughout his career, made him a symbol of Chicago blues around the world and an upholder of its noblest traditions.

Magic Slim — who was born Morris Holt in Torrence, Miss., on Aug. 7, 1937 — died Feb. 21 at a hospital in Philadelphia at age 75, after undergoing surgery for a bleeding ulcer, according to his son, Shawn Holt.

“He never sacrificed what his music was about,” said Jerry Del Giudice, co-owner of Blind Pig Records, which began recording Magic Slim in 1990 and continued to do so through his final release, last year’s “Bad Boy.”

Magic Slim’s — or Mr. Holt’s — music “was Mississippi mud,” Giudice said. “He electrified Mississippi blues. And he stuck with it. He was no rock-and-roller.”

Like generations of Southern bluesmen who migrated to Chicago in the mid-20th century, Mr. Holt lived the hard life he sang about. As a child working the cotton fields of the rural South, he couldn’t afford a guitar, so he made one by taking baling wire, nailing it to a wall and coaxing a primordial music from it.

He tried the piano, but when he lost the pinkie finger on his right hand in a cotton-gin accident, he focused on guitar, playing gigs when he wasn’t working in the fields.

In Grenada, Miss., where he moved at age 11, he met another future star of Chicago blues: Magic Sam, who anointed Mr. Holt “Magic Slim,” a reference to his towering height of more than six feet.

Mr. Holt first moved to Chicago in 1955 but returned to Mississippi to work on his music. He recorded his first single, “Scufflin’,” in 1966 and formed the Teardrops with his younger brothers a year later.

He took up residence at Florence’s, a South Side club, in 1972 and became a Chicago institution. He cut his first album, “Born Under a Bad Sign” (1977), for a French label and in the next decade recorded regularly for Alligator, Rooster Blues and Wolf Records.

“Gravel Road” (1990), his first recording for Blind Pig Records, took its title cut from one of the songs he played in childhood on his self-made guitar.

He maintained a high level of artistry for more than two decades, earning critical accolades for recordings such as “Scufflin’ ” (1996), “Black Tornado” (1998), “Snakebite” (2000) and “Raising the Bar” (2010).

Magic Slim and the Teardrops won the Blues Music Award for Blues Band of the Year in 2003. In recent years, he lived in Lincoln, Neb. Survivors include his wife, Ann Holt; and five children.

“He was a genius at what he did,” said veteran Chicago blues musician Billy Branch. “Nobody did it like Slim.

“It was just raw, unadulterated Chicago blues.”