The bluesman James Cotton was the son of a sharecropping Mississippi Baptist preacher and a mother who played the harmonica. And when they died when he was quite young, he picked up his mother’s harmonica and used it to play his way out of the cotton fields that gave him his last name.

Before Cotton was done — he died in 2017 — he’d more than lived up to his billing as Mr. “Super Harp.” He was a Grammy winner who played many of the major music festivals of his era, opening for The Who, The Doors and the Grateful Dead, headlining his own blues club in Chicago, touring his James Cotton Blues Band with The Steve Miller Band and introducing generations of rock fans to the music that gave birth to their music.

“Bonnie Blue: James Cotton’s Life in the Blues” is a loving musical appreciation of one of the last of his generation of bluesmen. We hear James Cotton lore, much of it related by his fans and two of the significant women of his life, who tell us how he learned by copying Sonny Boy Williamson II on “The King Biscuit Flour Hour” on the radio, performing in the cotton fields of the Bonnie Blue plantation he grew up onn near Tunica, Mississippi.

He met Sonny Boy, joined his band, and we hear from archival Cotton interviews the colorful anecdote about how the elder statesman of blues harmonica singers/players passed that band on to too-young-to-handle-it James.

Cotton would copy from and improvise around “every song on the jukebox” and every contemporary harp player he heard — Little Walter, Harmonica Shorty, Junior Wells and Sonny Boy included. When rock’n roll arrived, he adapted, and his passionate, animated stage show made him an in-demand opening act for all the American and British bands that grew up idolizing Howlin’ Wolf, Muddy Waters and that generation of bluesmen.

“Bonnie Blue” is filled with fans who were inspired to take up the blues by his example, Annie Raines among them.

“That sound has a heritage, the spirit of the (Mississippi) Delta,” she tells us.

Filmmakers Bestor Cam and Mike Majoros build their documentary around a Narrows Center (Fall River, Massachusetts) concert appreciation of Cotton, one of several he was honored with during his lifetime, and after he died.

A roundtable of players, members of Cotton’s Blues Band and others, reminisce.

And the filmmakers rounded up Buddy Guy, Keb’ Mo’ and Bobby Rush to place Cotton’s talent on the “Mount Rushmore” of the blues, and Steve Miller, Jimmie Vaughan and others back up his “blues gangster” reputation. Cotton packed a pistol because he was “shot five times” at one point, allegedly by the husband or boyfriend of a woman Cotton was stepping out with.

“Mistaken identity” a couple of interviewees suggest. Or maybe not, others wink.

Either way, in “Bonnie Blue” Cotton comes off as both a virtuoso and a something of a character, falling down the usual musical potholes — cheating management, alcohol and drugs — only to re-emerge, re-ignite his career and cement his reputation as he put in more decades of educating the world’s youth after his “music with a (Delta) heritage.”

Rating: unrated

Cast: Bobby Rush, Keb’ Mo’, Steve Miller, Buddy Guy, Jimmie Vaughan, Annie Raines, Billy Branch, Jacklyn Cotton and James Cotton.

Credits: Directed by Bestor Cam, scripted by Mike Majoros. A Freestyle release.

Running time: 1:27