The fabled Robert Johnson took Robert Junior Lockwood under his wing as his stepson in the late 20s or early 30s; since Johnson’s death in 1938, the personal and musical spirits of the two men have been inextricably intertwined. Lockwood, however, is no Delta clone; through the years he’s developed a reputation as one of our most relentlessly exploratory bluesmen, constantly moving into new realms of musical expression. Lockwood’s own compositions (“Little Boy Blue,” “Black Spider Blues”) are notable for their slow-burning heat, outrageous sexual innuendos, and underlying aggression. In recent years he’s been criticized for watering that rootsy blues intensity down with restless forays into pop and jazz; these days his set is as likely to include a nightclubby version of “Misty” as it is to feature a re-creation of one of his own standards or a Delta classic from stepfather Johnson. But although the stylistic jumps can be jarring, Lockwood plays everything with deep feeling and flawless musicianship, and he’s among the true living links to the legendary past of the blues. Tonight through Sunday, Rosa’s, 3420 W. Armitage; 342-0452.