Some artists are influential because so many followers try to imitate them; others are influential precisely because they cannot be imitated. Lightnin' Hopkins was of the latter variety. With a career that stretched from the 1920s through the '70s, the Texas bluesman was a genre unto himself, a deft guitarist equally at home in a quiet solo performance or fronting an electrified boogie band. He was a free-associating poet who made up entire songs on the spot, and a leathery-voiced singer whose vocals simultaneously communicated a lifetime of misery and an endless reserve of self-confidence.