The wistfulness, the wit, the elegant "rightness"--and the essential hopelessness--of these couplets from the 1926 song "Where's That Rainbow"" are immediately identifiable:

In each scenario,
You can depend on the end
Where the lovers agree.
Where's my Lothario"
Where does he roam, with his dome
Vaselined as can be"

These lines can have come from the lyrical lexicon of only one writer: Lorenz Hart. At once irrepressible and sad, insouciant and tragic, reckless and withdrawn, cocky yet insecure, brilliant but unreliable--a kaleidoscope of conflicting inclinations that were simultaneously the wellsprings of his genius and the roots of his downfall--he was one of the most erudite, sophisticated, and talented writers ever to have addressed the subject of the popular song. Yet, more than a century after his birth, he remains nearly forgotten by the general public, the greater part of his work seemingly fated to be forever overshadowed by...