Ry Who-der? Alex Wolfe’s documentary Santo Domingo Blues adroitly traces a noble history of bachata—a formerly ignoble Dominican musical form—while feeling intimate all the same. Warm’n’fuzziness is lent by the genre’s impossibly humble and genial “Supreme King,” Luis Vargas, our guide from Santiago and Santa Maria to South Williamsburg. Bachata is quintessential Quisqueyana, but wasn’t always so. Bachateros were maligned for years by the D.R.’s upper crust for playing “musica del bajo mundo” (“underground music,” one among other less euphemistic terms), and ridiculed by some D.R.-to-N.Y. transplants for making “crybaby music,” bachata being thematically infused with lost love and unresolvable bitterness. But hey, bitterness is contagious, and so is the music’s sugary three-chord twinkle. Wolfe’s anecdotal musicology succeeds precisely because of its bare-bones, bawdy yet beautiful approach—just like the music Vargas makes.