Bobby Rush scored just one hit single -- "Chicken Heads," which went to 34 on the R&B charts in 1971 -- but, then again, his career coincided with the slow sunset of blues being a charting concern. He started recording on his own in 1967, just as soul-blues -- a grooving, horn-spiked hybrid popularized by B.B. King and Bobby "Blue" Bland -- started to rise but he also spent some time up in Chicago, playing a bit with Muddy Waters and Jimmy Reed, urban connections that rarely surfaced in his music of the '70s, '80s, and beyond. What Rush specialized in was groove. He pushed soul-blues into previously uncharted funky territory, working that groove so hard he sometimes wound up in the province of disco. This suggests how Bobby Rush slyly adapted to the times while never seeming to pander, an ability that's showcased in Omnivore's wildly entertaining and illuminating four-disc history, Chicken Heads. Styles change -- he gets down and dirty with Chicago shuffles, he layers on horns just a few years later, he plays with disco until it passes, synthesizers come into vogue, he even rides some of the neo-roots movement of the 21st century -- but Bobby Rush remains the same, always a bold, bawdy singer who nevertheless is cannier than his ribald reputation suggests. Rush not only knows how to ride the rhythms but he slides into a song, which is why his soul-blues isn't just funk but also sexy. He enjoys playing with both the groove and his phrasing, and that's what gives the music serious life when the surroundings are super slick...which they often are, particularly in the records from the '80s and '90s. On an individual album basis, that clean, glossy sheen can be too glaring but when it's distilled into this history, it's appealing because it's seen in the context of an artist who's constantly on the move, constantly finding ways to adapt to what's hot without ever losing sight of who he is. That's a story that can only be told on a box set and that's why Chicken Heads is so valuable: it shows all the ways Bobby Rush kept the blues alive.