One afternoon last winter, two ships lined up side by side in a field of pack ice at the mouth of the Ross Sea, off the coast of Antarctica. They belonged to the Sea Shepherd Conservation Society, a vigilante organization founded by Paul Watson, thirty years ago, to protect the world’s marine life from the destructive habits and the voracious appetites of humankind. Watson and a crew of fifty-two volunteers had sailed the ships—the Farley Mowat, from Australia, and the Robert Hunter, from Scotland—to the Ross Sea with the intention of saving whales in one of their principal habitats. A century ago, when Ernest Shackleton and his crew sailed into the Ross Sea, they discovered so many whales “spouting all around” that they named part of it the Bay of Whales. (“A veritable playground for these monsters,” Shackleton wrote.) During much of the twentieth century, though, whales were intensively hunted in the area, and a Japanese fleet still sails into Antarctic waters every winter to catch minke whales and endangered fin whales. Watson believes in coercive conservation, and for several decades he has been using his private navy to ram whaling and fishing vessels on the high seas. Ramming is his signature tactic, and it is what he and his crew intended to do to the Japanese fleet, if they could find it.

Watson is fifty-six years old, pudgy and muscular. His hair, which is white, often hangs over his eyes in unkempt bangs. During trips to Antarctica, he usually grows a beard or a goatee. On January 19th, the day he moored his ships together in the Ross Sea, he wore a black, military-style sweater adorned with Sea Shepherd patches, and a rainbow-colored belt that held a sheathed knife. Watson was captaining the Farley, a rusty North Sea trawler built in Norway in 1958. The ship, black with yellow trim, featured a skull and crossbones painted across its superstructure and, on the forward deck, a customized device called “the can opener”: a sharpened steel I-beam that is propelled outward from the ship’s starboard side and is used to scrape the hulls of adversaries. Watson’s plan was to transfer as much furniture, equipment, and crew as he could from the Farley to the Hunter, in part because the Farley was old and barely seaworthy, in part because it was operating illegally and could be confiscated upon entry into port, and in part to ready it for a procedure that he called Operation Asshole—so named because it involved ramming one vessel into another’s stern.

When Watson is separated from land, he tends to behave like Captain Nemo, which is to say that he does what he thinks is right, even if it involves a violation of custom or the destruction of property. There are a number of rules belonging to civilization that outrage his sense of morality, among them the 1982 United Nations Convention on the Law of the Sea, which asserts that sovereign states alone are the ocean’s enforcers. If such rules interfere with his agenda, then, as far as he is concerned, rules be damned. This is particularly true when whales are at issue. Watson believes that whales are more intelligent than people, and that their slaughter is tantamount to murder. (He once compared their extermination to the Holocaust.) The Japanese take a different view. They have been hunting whales with a modern industrial fleet since the nineteen-thirties, and the more resolutely the rest of the world condemns their hunt the more adamantly their government seems to support it. Watson maintains that if his opponents are forced to defend their actions in public they will demonstrate the untenable nature of their position. A key part of his strategy is to force the issue.

Whaling is not banned, but it is not exactly permitted, either—an ambiguity resulting from political compromise and shortsightedness. In 1946, the world’s major whaling nations formed the International Whaling Commission to manage the world’s whale fisheries. It did a terrible job. By the nineteen-seventies, several species were nearing extinction, and by the early eighties the I.W.C. decided that commercial hunts should be halted. This is often referred to as the “ban” on commercial whaling, but it is more accurate to call it a moratorium. Even so, several leading whaling countries declined to abide by it. Whaling for the sake of science has always been permitted anywhere and without restrictions. The Japanese say that they are hunting whales off Antarctica in order to ascertain when there will be enough to harvest for profit. In the winter of 2005, they killed more than a thousand, nearly double the commercial catch of Norway, which rejected the moratorium. The Japanese fleet is run by the government-subsidized Institute for Cetacean Research, in Tokyo, but the institute has produced virtually no research of any regard, and all the whales that are purported to be under study are also butchered for the purpose of selling whale meat to the Japanese public.

Watson has a tendency to see things in their essence rather than in their particulars. A diplomat might say that the Japanese whaling fleet is technically complying with the rules of the I.W.C., and that to stop it one must first upset the status quo that permits the fleet to hunt whales. Watson, who cannot be bothered with the legal nuances of international regulations, insists that the Japanese fleet is breaking the law, and that, because the I.W.C. refuses to act, he and his crew must. He calls his fleet Neptune’s Navy, and he regards it as a law-enforcement agency. Moments before ramming a vessel, Watson will radio its captain and say something that sounds very official, such as “Please remove yourselves from these waters. You are in violation of international conservation regulations.” At times, he loses his cool. “We’re no protest ship,” he once told an intransigent captain. “Now, get out of here.” His sense of urgency, his impressive ego, his argumentativeness, his love of theatrics, his tendency to bend the truth, his willingness to risk lives or injury for his beliefs (or for publicity), and his courage (or recklessness) have earned him both loathing and veneration from those who are familiar with his activism.

Watson’s celebrity supporters, some of whom he has come to know personally, include Mick Jagger, Pierce Brosnan, Sean Penn, Aidan Quinn, William Shatner, Edward Norton, Orlando Bloom, and Uma Thurman. In 1995, Martin Sheen travelled with Watson and other activists to the Magdalen Islands, in Quebec, to protest the clubbing of baby seals. The group was threatened by a mob of angry sealers, and Watson was badly beaten. “He’s one of the gutsiest guys on the planet,” Sheen told me. “I am just so grateful to him for his commitment and his courage and his daring and his humanity.” Steve Wynn, the Las Vegas casino magnate, once helped Watson buy a submarine (though it was missing essential parts and so couldn’t be used). John Paul DeJoria, the C.E.O. of John Paul Mitchell Systems, the hair-care-products company, has raised tens of thousands of dollars for Watson’s campaigns. Sea Shepherd’s board of advisers includes Elizabeth May, the leader of Canada’s Green Party, and Roger Payne, one of the world’s foremost experts on whales. Watson is portrayed as a savior in the fiction of Edward Abbey, the author of “The Monkey Wrench Gang” (1975), a seminal book for eco-saboteurs. The Dalai Lama has given him a written endorsement and a statue of Hayagriva, a wrathful deity who, according to early Buddhist texts, yells with a “dreadful voice” and “subdues all demons and all evils.” Within the animal-rights community, Watson is treated like a demigod. “I think he’s a hero,” Peter Singer, the Princeton ethicist and the author of “Animal Liberation,” told me. “He’s been prepared to put himself on the line to stop the abuse of animals in places where no one else was prepared to go.”

Watson’s detractors are no less adamant. Officials in Iceland, Denmark, Norway, Japan, Canada, and Costa Rica have denounced him; some have even called him a terrorist. In the mid-nineties, Norway convicted him of attempting to scuttle a whaler named Nybræna, and he spent eighty days in prison. “He is persona non grata in Iceland,” Kristján Loftsson, the managing director of Hvalur, Iceland’s largest whaling company, told me. Watson has made enemies of other conservationists, too. For decades, Greenpeace has wanted nothing to do with him—a rebuke that is particularly stinging because he was a founder of the organization. Last year, Watson resigned from the Sierra Club’s national board, after feuding with other members about the group’s policies. He has been barred from I.W.C. meetings since 1986, when Sea Shepherd scuttled two of Hvalur’s ships in Reykjavik’s harbor—an act of sabotage that many conservationists believe helped turn Icelandic public opinion against the cause of saving whales. Sidney Holt, one of the principal architects of the whaling moratorium, told me, “I think his involvement in all this is an absolute disaster. Almost everything he has been doing has had blowback for those who want to see an end to whaling. In too many cases, playing piracy on the ocean, and creating danger for other ships, is simply not liked.”