I remember the first time I heard that voice. A suitemate in college, a Pennsylvanian, was blaring “Who Killed Davey Moore” from the back room, the nasally wail filling the air like paint fumes. From the front room, Ernie, from Perquimans County, North Carolina, couldn’t take it anymore. “Turn that crap off!” he hollered, to no avail.

I didn’t know who killed Davey Moore, but I felt as though the question was being directed at me. My reaction to hearing Bob Dylan for the first time was more intrigue than annoyance, a sort of surprise that anyone with a voice like that could get a recording contract, much less become famous. I was a latecomer to Dylan’s music, and despite a college friend’s proselytizing, it did not take at first. I assumed it was—like coolness—something for other people.

I don’t know when exactly it did begin to take, but within a few years I had Oh Mercy (1989) in heavy rotation. I turned to it first not because of Dylan himself but because of the record’s producer, Daniel Lanois. The album is moody, atmospheric, dark—haunted, one might say, by “The Man in the Long Black Coat,” who seems to stalk the borders of Oh Mercy with brooding menace.

Somebody seen him hanging around
At the old dance hall on the outskirts of town
He looked into her eyes when she stopped him to ask
If he wanted to dance, he had a face like a mask
Somebody said from the Bible he’d quote
There was dust on the man
In the long black coat

He seems to have walked right out of a Flannery O’Connor story and into a Bob Dylan song, bearing on his bent back all “the pulse and vibration and the rumbling force” of a world seething with dark mystery. He presages the apocalyptic melancholy of the album’s final song, “Shooting Star”:

It’s the last temptation, the last account
The last time you might hear the sermon on the mount
The last radio is playing

By the time of Oh Mercy, Dylan had cruised into a winsome world-weariness, and his voice was starting to show cracks. That album marks Dylan’s transition into a new vocal signature—the gargling sage. Since then, his voice has become so distinct that it is no longer possible to imitate it.

No other American singer has tried on as many voices as Dylan has. His early albums owed a lot to Woody Guthrie, both in terms of material and vocal style. Within a few years, Dylan changed tack, to the smoke-free country voice of John Wesley Harding and especially Nashville Skyline. There he sang from a different part of the throat, farther back, as if reaching deeper into the confused tangle of the American musical psyche. A decade later, there was the Budokan voice, then the albums from the 1980s, such as Infidels, in which the old folk twang from Greenwich Village is still just barely audible. But by then the cracks in the larynx were beginning to appear. By the 1990s the old voice was almost entirely gone.

In 1997, Dylan released Time Out of Mind, his first collection of original music since Oh Mercy and also produced by Daniel Lanois. When Time Out of Mind opens with “Love Sick,” the voice is a haunting whisper-echo of what it once was. More and more, it is a steel rake dragged behind a V-8 Ford truck on a loose gravel road. But it also sounds controlled: every crack and gurgle precisely placed, the alternating timbre of tenderness and harshness, darkness and light, intentional. At the end of each line of “Not Dark Yet,” Dylan’s voice trails off:

Well, I’ve been to London and I’ve been to gay Paree
I’ve followed the river and I got to the sea
I’ve been down on the bottom of a world full of lies
I ain’t looking for nothing in anyone’s eyes
Sometimes my burden seems more than I can bear
It’s not dark yet, but it’s getting there

In his two most recent albums of Sinatra covers, Shadows in the Night (2015) and Fallen Angels (2016), the familiar scratch in the throat emerges only rarely from underneath the gliding, wee-hour cadence of the vocals, like a sudden crackling ember from the steady fire that seems to burn warm but not hot throughout both of these albums. The voice—self-possessed, unhurried, settled-in—is that of a lover who neither needs nor desires to go anywhere.

One of Dylan's more remarkable but less recognized achievements is the now-defunct Theme Time Radio Hour, an old-school variety show that ran on new-school satellite radio from 2006 to 2009. For each one-hour episode, Dylan curated a repertoire of songs organized around a single motif. He adopted a special, hitherto untried voice: the radio DJ. Listening to the program, one became aware just how much control over his voice Dylan really has. The uninitiated listener who stumbles upon Love and Theft or Modern Times might have the impression of a singer who has lost mastery over his own wild instrument—a singer who, despite his efforts to corral his voice into something intelligible and vaguely melodic, has yielded to the inevitable depredations of age. But Theme Time shows Dylan in utter control, and the voice has accrued a sort of sonic patina of hard-earned wisdom, the timbre of worn truth. Theme Time, probably the best thing that satellite radio ever gave us, offers Dylan a chance to strut his archivist-scholar persona. His knowledge of the American Songbook is encyclopedic: in the first episode, on the theme of weather, he summons the voices of Muddy Waters, Jimmie Davis, Jimi Hendrix, Sister Rosetta Tharpe, Stevie Wonder, Frank Sinatra, the Staple Singers, and the Carter Family. It’s a thematic snapshot of American music in all its bright and vast array.

Dylan seems to bear these other voices within his own. They rattle together in his protean growl. He has given almost as much attention to the American tradition in popular music as he has to his own original songwriting, whose roots burrow deep into the soil of that tradition. All the borrowing from other artists has, paradoxically, made Dylan’s voice unique. It has only improved with age—that nasally snarl, that gravelly croak, that rock grinder in his larynx. It is an American river: stony, deep, muddy.

His influences are as vast as the Mississippi, and he has openly acknowledged his debt to them, frequently recording (as in his last two albums) collections of covers made famous by other artists before him. Dylan’s corpus is ecumenical in its ambition to leave nothing out. Much of its uniqueness consists in a refusal to stay put, a relentless quest for surprise. Even a finished song is never really complete: what you hear on the album recording may be nothing like what you hear in concert. In a live performance now, it may be a few bars before you realize that what you’re hearing is “Tangled Up in Blue,” as strange and alive as it ever was. Dylan is a particularly nomadic sort of minstrel, wandering the American musical landscape without ever getting lost, and the forward thrust of his songwriting has always been proportional to the depth of his musical memory. He is always one step ahead of his audience, and one step behind.

When he was awarded the Nobel Prize for Literature, there was no shortage of understandable grumbling from poets and writers who questioned whether Dylan’s body of work counts as literature. Even if it does, they wondered aloud, was it worthy of the award? It may be true that, read on the page, without the music, Dylan’s lyrics do not compare favorably with the work of other great contemporary writers. But those lyrics cannot be separated from the organism of song. Taking them on their own is like taking the heart out of a body and laying it on the examining table. Even if it could still beat on its own, what good would it be? It is easy to understand why Dylan’s lyrics have been so celebrated—for one thing, it gives those who don’t like his voice something else to admire. But Dylan is not just a writer or a singer. And his voice is not only unique. It is a tradition.