Jim Cullum, a jazz cornetist, bandleader and educator who became a flamekeeper of traditional jazz, and whose San Antonio-based ensemble became a mainstay of public radio on the weekly program “Riverwalk Jazz,” died Aug. 11 at his home in San Antonio. He was 77.

The cause was an apparent heart attack, said his booking agent, Steve Frumkin.

Even as a teenager growing up in Texas in the 1950s, when his peers adopted greasy, ducktail hairdos and twisted their hips to Elvis, Mr. Cullum was drawn to his father’s collection of 78s featuring Louis Armstrong and Bix Beiderbecke and other Jazz Age luminaries. At 14, he saved up $7 to buy his first cornet — a beat-up 1920 model he spotted in the window of a pawnshop — and didn’t look back, except in his musical repertoire.

As an enterprising youth, he formed a quartet that played outside a Dairy Queen. “We got four lines of credit,” he once recalled, “and got paid in ice cream cones, milkshakes and hamburgers.” Most prominently through the San Antonio-based Jim Cullum Jazz Band, he devoted his career to resurrecting music popularized by the likes of Beiderbecke, Armstrong, King Oliver, Jelly Roll Morton and Sidney Bechet.

Mr. Cullum threw a musical life jacket to a genre nearly submerged by later jazz styles, including big band, bebop and jazz-rock fusion, not to mention rock, rap and generations of pop.

Jazz scholar Dan Morgenstern said Mr. Cullum, whom he called a top-flight musician, was not alone in seeking to preserve traditional jazz, but that his prominence on public radio put him in the pantheon of “trad-jazz” bandleaders.

“The skill lies in not making the music sound like a reproduction of an antiquated style, but in keeping it lively and fun, and he did that,” Morgenstern said. “You keep it alive by making it sound alive.”

Mr. Cullum, who had long operated the Landing jazz club on San Antonio’s River Walk promenade, attracted an all-star lineup of musicians including clarinetist Allan Vaché and pianist John Sheridan, as well as guest players such as pianist Dick Hyman, trumpeter Clark Terry, vibraphonist Lionel Hampton and clarinetist Bob Wilber.

The band’s shows were featured on regional radio outlets before Public Radio International distributed the weekly series “Riverwalk: Live From the Landing” (later renamed “Riverwalk Jazz”) from 1989 to 2012.

In addition to the airtime, the band played the festival circuit and had engagements at high-profile venues including New York’s Carnegie Hall and Washington’s Kennedy Center. The group released dozens of albums, including a 1987 instrumental version of the Gershwin folk opera “Porgy and Bess,” which Mr. Cullum said was his favorite recording. Reviewing the album for The Washington Post, critic Mike Joyce praised its “subtlety and verve.”

“We’re not preservationists,” Mr. Cullum once told the Dallas Morning News. “It’s just good, timeless music. I love it and hope we can breathe new life into it.”

James Albert Cullum Jr. was born in Dallas on Sept. 20, 1941, and moved to San Antonio at 12. His father, who ran his family’s wholesale grocery business, also was a reedman who jammed with visiting musicians including Jack Teagarden and Jimmy Dorsey.

In 1962, father and son formed what was then known as the Happy Jazz Band and, the next year, opened the Landing, one of the first music clubs on the River Walk. “It was very charming,” Mr. Cullum later told the San Antonio Express-News. “You could squeeze 200 people in there, break all the fire codes.”

The club moved several times before relocating in 1982 to the new Hyatt Regency, along the River Walk. Mr. Cullum, who renamed the band after his father’s death in 1973, sold the Landing in 2009 and stopped recording new “Riverwalk Jazz” programs in 2012. Past shows are archived online through the Stanford University Libraries at riverwalkjazz.stanford.edu.

Mr. Cullum was on the faculty of the Stanford Jazz Workshop, a leading forum for jazz education, from 1993 to 2005. As board member and president of the San Francisco Traditional Jazz Foundation, he was instrumental in helping create a digital exhibit at Stanford to showcase the history of the region’s traditional jazz scene.

He continued leading a band until his death, performing several times a week. A list of survivors was not immediately available.

“We’ve done well, and we’ve had our successes,” Mr. Cullum told the Morning News. “But I don’t think of it as hitting the big time. We’re just doing what we’ve always done. I’d be doing it no matter what.’ It’s like what Louis Armstrong said, ‘Don’t tell no one, but I’d do it all for nothing.’ ”