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

Slim — who was born Morris Holt in Torrence, Miss., on Aug. 7, 1937 — died Thursday in 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 Slim in 1990 and continued to do so through his final release, last year’s “Bad Boy.”

Slim recorded his first single, “Scufflin’,” in 1966, forming the soon-to-be-celebrated Magic Slim and the Teardrops (with his younger brothers) in 1967. He cut his first album, “Born Under a Bad Sign” (1977), for a French label.

“Gravel Road” (1990), his first recording for Blind Pig Records, took its title cut from one of the songs he played in childhood on a self-made guitar. He earned critical accolades for recordings such as “Scufflin’ ” (1996), “Black Tornado” (1998), “Snakebite” (2000) and “Raising the Bar” (2010), which marked his 20th anniversary on Blind Pig.

Magic Slim and the Teardrops won the Blues Music Award for Blues Band of the Year in 2003, one of several Blues Music Awards it aced.