Led by the heroically sideburned Ray Dorset, Mungo Jerry rose to overnight fame with their debut single, 1970's "In the Summertime," a loose-limbed celebration of the carefree summer months set to a rollicking acoustic accompaniment that invoked the sounds of skiffle and jug band music in its playful approach to the blues. "In the Summertime" would become and remain their signature song, but it was also the basis for a long and successful career for Dorset, who continued to tour and record under the Mungo Jerry banner half-a-century after the band made their debut. The playful...