Director Don McGlynn has been in the business of making heartfelt, low-budget documentaries of important but marginalized musicians for 20 years now. Performers such as Art Pepper, Charles Mingus and Harold Arlen -- all monumentally influential and under threat of being footnoted -- have had their legacies bolstered by McGlynn's films. Now, the impact of Chester Burnett, aka Howlin' Wolf, can be equally measured. Though Wolf's probably not in danger of being forgotten, it would be a tragedy if he were to be solely remembered as "the black guy who played with Clapton and those other British cats." This film, expanded by 30 minutes from its original one-hour length, celebrates both Wolf's ambassadorial impact on rock audiences and his relevance to blues traditions. Without overly idealizing Wolf's Mississippi upbringing, McGlynn makes it abundantly clear that despite his crossover appeal, Howlin' Wolf was a to-the-bones bluesman during his four-decade career. Long-lost performance footage pads a substantial bonus section on the DVD, virtually eclipsing the theatrical release of the movie.