Drummer Al Jackson was an American institution, putting the beat behind Al Green classics, driving Booker T. & The M.G.’s, and propelling a host of Stax soul acts. Whether he was playing the sexiest triplets in history behind Green’s sensual “Let’s Stay Together” or giving the simmering groove of Booker T. & The M.G.’s “Green Onions” the deepest pocket ever, Jackson knew how to let the music breathe.