Willie Nelson’s history boasts all the easy navigability of an iceberg. Nelson has dabbled in practically every genre over the course of his career, though he plays it fairly straight on his new album, Heroes, a classic country covers record with a few originals thrown in. But the man is still a musical wildcard, as his richly varied discography attests. Grasping that inevitably means plunging further and further back to his first break in ’60s Nashville, or at least to the ’70s albums (Red Headed Stranger, Shotgun Willie, etc.) that made him huge. Nelson continues to record and perform tirelessly and, with the death of Johnny Cash, he stands as an ambassador of the American songwriting tradition that he helped innovate.