Short answers, pulled from the story.
Moby-Dick is an 1851 novel by Herman Melville in which sailor Ishmael narrates the voyage of the whaling ship Pequod, whose captain, Ahab, obsessively hunts the white sperm whale that bit off his leg. The novel blends adventure with cetology, philosophy, and Shakespearean tragedy.
Moby-Dick was a commercial failure when it appeared in 1851. It went out of print, and Melville died in 1891 without seeing it celebrated. Its reputation as a Great American Novel was established only in the 20th century, after the 1919 centennial of Melville's birth.
Two actual events shaped the plot. In 1820, a sperm whale rammed and sank the Nantucket ship Essex some 2,000 miles from the western coast of South America. In the late 1830s, an albino sperm whale called Mocha Dick, said to have around 20 harpoons in his back, was reported killed in waters off the Chilean island of Mocha. Melville drew on both incidents.
Melville met Hawthorne on the 5th of August, 1850, at a picnic near Lenox, Massachusetts, when the manuscript was perhaps half finished. Reading Hawthorne's Mosses from an Old Manse led Melville to compare it to Shakespeare. The novel is dedicated to Hawthorne "in token of my admiration for his genius." Many scholars believe the encounter deepened the book's ambition.
The most important source was Thomas Beale's Natural History of the Sperm Whale, published in 1839, which Melville purchased on the 10th of July, 1850. Scholar Steven Olsen-Smith writes that in "scale and complexity" its significance to the composition of Moby-Dick surpasses every other source book Melville used.
The opening sentence is "Call me Ishmael." It is among world literature's most famous first lines and introduces the sailor who narrates the entire novel.