Irish rock titans U2 are one of the biggest bands in the world. Catapulting over their peers after the release of The Joshua Tree in 1987, they have maintained their status well into the 21st century. Alone among all the groups to emerge from the post-punk era, U2 channeled their yen for moody, experimental aural textures into clearly defined rock anthems and ballads -- songs that sounded majestic yet felt personal. Much of that sense of intimacy can be attributed to Bono, a lead singer who gravitates toward grand gestures yet remains grounded by his belief in humanity and the...