John Gould was one of the most sought-after taxidermists in 19th-century London, commissioned by King George IV to stuff the first giraffe to arrive in England.

But Gould’s lasting legacy is birds. He travelled the world documenting and cataloguing as many avian species as he could find, many of them never seen before, earning him the nickname the Bird Man and the appointment as official “bird stuffer” to the Zoological Society.

Gould commissioned a series of beautiful paintings from his notes and sketches of birds he discovered – including specimens brought back to Britain in 1836 by Charles Darwin, after his expedition on HMS Beagle.

Next week, an extremely rare set of folios containing all the illustrations will be presented at a rare book fair in London with a £2m price tag.

Pom Harrington, owner of books dealer Peter Harrington and chairman of Firsts, the rare book fair which takes place at the Saatchi Gallery in London from 16-19 May, said it is almost unheard of for a full set of the folios to be found in one collection. This is the most complete set to come to market.

“Gould’s oft-reproduced illustrations of birds are among the finest ever executed,” he said. “As they were published across six decades in the 19th century, the folios are rarely found gathered together, and as such, seldom come to market as a set.”

The set of uniform-bound books also contains volumes on the mammals of Australia, where Gould, who died in 1881 aged 76, travelled in 1838.

Harrington added: “The scarcity of such complete collections, particularly those bound magnificently and uniformly by distinguished London binders like Zaehnsdorf, drives the significant market value of this exceptional set.”

Gould was born in Lyme Regis, Dorset, in 1804. The son of a gardener, he set up his taxidermy business in London in his 20s. It is thought he was inspired to create his illustrated catalogue of birds after a collection of birds, many previously undiscovered species, arrived from the Himalayas at the Zoological Society’s museum. Around the same time, poet and artist Edward Lear published an illustrated book on parrots which proved immensely popular in the 1830s.

Gould employed a number of artists to work from his notes and sketches, beginning with his wife, Elizabeth Gould, then Lear, and others including Henry Constantine Richter, William Matthew Hart and Joseph Wolf.

“While Gould never claimed he was the artist for these plates, he repeatedly wrote of the ‘rough sketches’ he made from which, with reference to the specimens, his artists painted the finished drawings,” Harrington said. “The design and natural arrangement of the birds on the plates was due to the genius of John Gould.”

Gould’s work on birds had an impact on Darwin’s theories of evolution. Gould’s biographer, Gordon Sauer, wrote in the Oxford Dictionary of National Biography that Gould had contributed the “bird” volume of Darwin’s Zoology of the Voyage of HMS Beagle. “In January 1837, Gould pronounced a group of 12 birds from the Galápagos Islands, which Darwin had thought to be ‘blackbirds, warblers, wrens and finches’, as all one family of finches, with variations in their beaks and size,” he wrote.

“This was the crucial piece of evidence that enabled Darwin to come to his theory of island speciation.”

The rare set of books for sale next week is thought to have been assembled by a ­collector or bookseller in the late 1880s or 1890s, after Gould’s death, and sold, Harrington said, as a “kind of trophy set”.

He added: “Unfortunately, the set has no marks of ownership, neither bookplates nor inscriptions.

“When it last appeared at auction at Christie’s in 1997, the set was described as being ‘probably purchased by an English client in the 1880s, from Gould and Sharpe, and bound uniformly under their directions’. This could be a bit of a reach, as Gould died in 1881, but may not be that far off the mark. ‘Sharpe’ is the ornithologist Richard Bowdler Sharpe, who worked closely with Gould in his later years.”

The volume sold then for £507,500 but the 1997 auction record described the set as simply “the property of a European collector”.

A bit of detective work by Peter Harrington, researching book sales in the 1890s, shows auction prices and purchasers for several Gould folios, which could be the same ones that form this set.

Harrington said: “We could perhaps speculate that it was offered en bloc to a wealthy client, although we will never know. As a personal opinion, the freshness and excellent condition of the set shows that it has not had many owners.

“It has clearly been well looked after in a library somewhere and not moved around regularly.”

• This article was amended on 5 May 2024 to make clear that John Gould commissioned the illustrations rather than creating them himself.