Run-D.M.C. leaves no doubt about its intent on King of Rock. The New York trio’s hard-hitting sophomore album begins with a statement of purpose (“Rock the House”) that serves as a stereophonic primer for the title track, a hybrid warning-anthem-theme song that swarms with justified boasts, heavy metal riffs, booming beats, cowbell accents, and dance-worthy grooves. The back-to-back tunes set the tone for a 1985 record that largely established the blueprint for the hip-hop that would follow for the next two decades — and which helped make rap a mainstream currency via the previously off-limits channels of radio, TV, and the national stage.