From BookJive

Ahab is the tyrannical captain of the Pequod who is driven by a monomaniacal desire to kill Moby Dick, the whale that maimed him on his last whaling voyage. A Quaker, he seeks revenge in defiance of his religion's well-known pacifism. Ahab's name comes directly from the Bible (see 1 Kings 16:28).

Little information is provided about Ahab's life prior to meeting Moby Dick, although it is known that he was orphaned at a young age. When discussing the purpose of his quest with Starbuck it is revealed that he first began whaling at eighteen and has continued in the trade for forty years, having spent less than three on land. He also mentions his "girl-wife" whom he married late in life, and their young son, but does not give their names.

In Ishmael's first encounter with Ahab's name, he responds "When that wicked king was slain, the dogs, did they not lick his blood?" (Moby Dick, Chapter 16).

Ahab ultimately dooms the crew of the Pequod (save for Ishmael) to death by his obsession with Moby Dick. During the final chase, Ahab hurls his final harpoon while yelling his now-famous revenge line:

... to the last I grapple with thee; from hell's heart I stab at thee; for hate's sake I spit my last breath at thee.

The harpoon becomes lodged in Moby Dick's flesh and Ahab, caught in his own harpoon's rope and unable to free himself, is dragged into the cold oblivion of the sea with the injured whale. The whale eventually destroys the whaleboats and crew, and sinks the Pequod.

Ahab has the qualities of a tragic hero – a great heart and a fatal flaw – and his deeply philosophical ruminations are expressed in language that is not only deliberately lofty and Shakespearian, but also so heavily iambic as often to read like Shakespeare's own pentameters.

Ahab's motivation for hunting Moby Dick is perhaps best summed up in the following passage:

The White Whale swam before him as the monomaniac incarnation of all those malicious agencies which some deep men feel eating in them, till they are left living on with half a heart and half a lung. That intangible malignity which has been from the beginning; to whose dominion even the modern Christians ascribe one-half of the worlds; which the ancient Ophites of the east reverenced in their statue devil; -- Ahab did not fall down and worship it like them; but deliriously transferring its idea to the abhorred white whale, he pitted himself, all mutilated, against it. All that most maddens and torments; all that stirs up the lees of things; all truth with malice in it; all that cracks the sinews and cakes the brain; all the subtle demonisms of life and thought; all evil, to crazy Ahab, were visibly personified, and made practically assailable in Moby Dick. He piled upon the whale's white hump the sum of all the general rage and hate felt by his whole race from Adam down; and then, as if his chest had been a mortar, he burst his hot heart's shell upon it.

References

Wikipedia