Samuel Langhorne Clemens may well have led a happier life if he had remained a steamboat pilot on the Mississippi. But then he never would have become Mark Twain — with all the heartache, frustration and dadgum bother (as he might put it) that job entailed.

It's that dark side, usually cloaked beneath Twain's legend, that dominates Ron Chernow's massive new biography. Following on his popular works about Hamilton, Washington and Grant, Chernow here documents Twain's failings, as well as his triumphs, in exhaustive fashion.

It is a rich life, to be sure. Chernow takes the first half of the book to cover the Twain we know best: the years in which the boy from Hannibal, Mo., becomes a printer, pilots a steamboat, enlists in the Confederate army, mines silver in Nevada and writes for a Virginia City newspaper.

He follows his first bestseller, "The Innocents Abroad," with marriage to heiress Olivia Langdon, builds an opulent mansion in Hartford, Conn., and proceeds to create "a literary voice that was wholly American," Chernow writes, "capturing the vernacular of western towns and small villages where a new culture had arisen."

Capable of great hatred and great empathy, by turns explosive and thoughtful, Twain at 60 had written the books for which we most remember him: novels about Tom Sawyer and Huckleberry Finn, "Roughing It," "The Prince and the Pauper," "Life on the Mississippi," on and on. At the same time, he had become the most popular lecturer of the era, delighting audiences here and abroad with his deadpan wit and homespun observations.

Alas, there was little to laugh about at home. The second half of the book documents Twain's final and unrelentingly dark 15 years, which saw him battling bronchitis (he smoked 40 times a day), gout and carbuncles, and fending off creditors made numerous by his extravagance (the reader will lose track of the number of homes the family rented in Europe, ostensibly to save money on their lifestyle in Hartford).

Mark Twain

He mourned the untimely deaths of two daughters and his devoted but fragile wife, who died at 58 of heart failure. A third daughter struggled with epilepsy. Always inclined to gloom, the narcissistic Twain berated himself for hastening their demise through his own negligence.

"Ah, this odious swindle, human life," he grimly scribbled in one of his notebooks.

Born with the Southern prejudice of his youth, he became an outspoken critic of racism against Black Americans (though not so much with American Indians); white people, he said, had "ground the manhood out of them, and the shame is ours, not theirs, and we should pay for it."

He loathed the slogan "Our country, right or wrong," calling patriotism "a word that always commemorates a robbery." Though he typically lined up with Republicans, he was appalled by friends who rushed to support corrupt GOP presidential nominee James G. Blaine, who favored higher tariffs, a ban on Chinese workers and extending the American flag abroad. "Isn't human nature the most consummate sham and lie that was ever invented?" he wrote.

Then there were Twain's quirks, what Chernow calls the "large assortment of weird sides to his nature." He comes off as daft for making disastrous investments in unpromising inventions, the most notable being an estimated $300,000 ($8 million to $10 million today) he sank into a maddeningly defective typesetter.

And it's hard not to think Twain creepy for his attraction to adolescent girls — "angelfish," he called them — whom he met in chance encounters and proceeded to romance with sweetly worded letters. Some consider his behavior that of a latent pedophile, though Chernow notes he was never accused of predatory conduct.

Twain was skeptical of biographies, saying they captured only "the clothes and buttons of a man" rather than the man himself. But he would be hard-pressed to make that case against Chernow. More than simply a book about America's seminal writer, this is a long and winding story about the quintessential American — clothes and buttons, mind and heart, warts and all.

Mark Twain

By: Ron Chernow.

Publisher: Penguin, 1,174 pages.