Heck cattle, a giant breed created by the Nazis, on a British farm in 2009. (Press Association via AP)

Some of Derek Gow's cows terrified him. "If I was standing here and some of the more aggressive ones were in this field, and they could see me, then they would come right across now and try and kill you," he told the BBC. Those cows would charge "with every intention of wiping you off the face of this Earth," he said from his farm.

That aggression was no fluke; those cows were Heck cattle, bred by Nazi zoologists who used Spanish fighting bulls in their quest to resurrect a long-extinct breed, the aurochs. Their resulting mean demeanor forced Gow, an English farmer, to send 20 of his Heck cows off to be turned into burgers and sausages, the BBC reported.

The story of how the Nazis got into the cow-breeding business actually began in 1600s Poland, when the last of the aurochs died. Dutch writer Cis Van Vuure said the aurochs had "the dubious honor of being the first documented case of extinction," Elizabeth Kolbert writes in the New Yorker.

These were wild cows with ancient roots. They adorned the walls of caves and are thought to have stood about six feet tall. Julius Ceasar said the beasts had extraordinary strength and speed and were "a little below the elephant in size," Kolbert writes, although she casts doubt that he ever actually saw one.

Competition from domestic breeds and over-hunting led to dwindling numbers. Eventually the aurochs disappeared from the European landscape.

That is, until the 1920s, when German zoo directors and brothers Lutz and Heinz Heck cooked up the idea to bring them back. They believed that the aurochs were the origin of all domestic cattle, Michael Wang writes for Cabinet Magazine.

Lutz Heck recalled that as a youth, he became keenly interested in the lowland European bison and aurochs, "which have become almost legendary but are regarded as the most powerful representatives of primeval German game."

By the 1930s, the Nazi government took an interest in the program and began funding it. Reintroducing aurochs "into the German landscape was part of a larger project of constructing a national identity based on mythic foundations," Wang writes.

Lutz Heck, "a committed Nazi," was eventually appointed to the Third Reich’s Forest Authority, Kolbert writes, adding, "his idea of breeding back the aurochs dovetailed neatly with the Nazis’ scheme of restoring Europe, through selective human breeding, to its mythic, Aryan past."

But without modern genetics, the brothers instead bred domestic cows in hopes of recreating features attributed to the wild aurochs. They were guided by old writing and images, including cave paintings, of the beasts, Wang writes. Each brother bred a set; Lutz Heck used Spanish fighting bulls.

One brother sent his cattle to modern-day Poland, and another set was sent to the estate of their Nazi research patron north of Berlin, Kolbert writes. But Allied bombs and the end of the war also meant the end for most Heck cattle.

"Animals succumbed to shrapnel wounds or burned to death in their cages. Dangerous species broke loose and were shot. Such was the fate of the Heck aurochs," Wang writes. "Lutz Heck’s son gunned down the agitated and stampeding aurochs, together with warthogs and wild boar, after they had escaped their burning enclosures."

While most died, some Heck cattle at the Munich zoo and other parks did survive.

Decades later, Gow — a farmer and conservationist — came into the picture. In 2009, he brought 13 Heck bulls and cows to his farm, the first time the animal set foot on British soil. He told the Guardian that the beasts "look prehistoric" and would be perfect for nature photographers. Gow was also interested in starting his own breeding program.

"They are an important part of the ecosystem because each cow produces its own weight in dung a year," Gow said in 2009. "That is excellent for the whole food chain, from dung beetles upwards."

Meanwhile, other breeders have become interested in the aurochs. The Heck cattle that come directly from the Nazi program aren't technically the aurochs of old, as they don't share the same genetics. They "will attack without a prior threat display," Henri Kerkdijk, who heads a Dutch preservationist group seeking to resurrect aurochs via genetics, told Time.

Gow, for his part, was able to breed the Heck cattle he owned. But after more than five years, many of the animals were just too aggressive to keep. He said they had little commercial value, although they were still important for conservation purposes.

"The ones we had to get rid of would just attack you any chance they could," Gow told the Guardian this week. "They would try to kill anyone. Dealing with that was not a lot of fun at all."

Even loading them onto a trailer to get rid of them was a challenge; a "very athletic young man" had to allow the beasts to charge at him as he stood on a ramp. Gow says that with the culling of the more violent animals, peace has returned to his farm.

"Despite these problems, I have no regrets at all," Gow told the Guardian. "It has been a good thing to do, and the history of them is fascinating."