Watch the Letter to Alfred online guitar lesson by David Hamburger from Essentials: Fingerstyle Blues
The chord changes here are pretty typical of the way jazz musicians might play through a twelve-bar minor blues. Take those changes, use the alternating thumb style to spell out the chords and drop in a minor pentatonic melody, and you’ve got the first eight bars of the tune. The tricky melodic business over the turnaround is also lifted from the jazz vocabulary, in that it outlines the sound of first a Bmin7b5 chord and then an E7b9 chord. Not that you need to know that to play it.