Wight wrote a series of semi-autobiographical novels under the pen name James Herriot, with Sinclair and Donald appearing in fictional form as brothers Tristan and Siegfried Farnon.

Tristan was portrayed as a charming rogue who was still studying veterinary medicine in the early books, constantly having to re-take examinations because of his lack of application, often found in the pub, and provoking tirades from his bombastic elder brother Siegfried.

In the following year, he enlisted in the Royal Army Veterinary Corps and married Sheila Rose, the only daughter of Douglas Seaton, a general practitioner based in Leeds.

Shortly after his marriage, he was posted to Haryana in India, and on demobilisation, he joined the Ministry of Agriculture's Sterility Advisory unit in Inverness, Scotland.

[4]: 109 [3] Sinclair's elder sister, Elsa Vaughan,[5]: 297  married Cyril Walter Russell on 5 June 1934 at St Robert's Catholic Church, Harrogate, where he gave her away.

[3] In his youth, Sinclair had considered a career in dentistry, but his interest turned to veterinary medicine after assisting his cousin, then a local veterinarian,[3] with bovine tuberculosis testing.

[7][8][a] He finally passed his professional examinations at Edinburgh in December 1943,[9] and in the same month, he was admitted a member of the Royal College of Veterinary Surgeons.

At the end of the war, he joined India's dairy programme,[11] supervising the care of seventy thousand water buffalo on military farms, and teaching pregnancy testing to local veterinarians.

[7] Alf Wight would write long letters to Sinclair, often twenty pages,[7] that would give news from home and would finish with a description of the Yorkshire countryside.

In 1950, the ministry offered him a transfer to the MAFF Veterinary Investigation Centre in Weetwood Lane, Leeds,[11] a diagnostic laboratory for veterinarians in Yorkshire.

"[11] In 1953, Sinclair and Ken Sellers, a veterinary colleague at the centre,[18][b] reported a cross-species infection of Salmonella typhimurium in shorthorn cows on a farm in Northumberland.

The farmers recorded the offspring of ewes and rams, and if they displayed symptoms of scrapie, then all affected sheep, including their relatives, would be culled from the flock.

[16] For example, in It Shouldn't Happen To a Vet there is an account of Sinclair letting a car run away and demolishing the local golf club hut.

So there was always that love-hate relationship between the two [brothers], very well portrayed in that first book.The 1975 film All Creatures Great and Small was the first adaptation of Wight's semi-autobiographical novels of James Herriot.

It was directed by Claude Whatham,[26]: 615  and starred Simon Ward and Anthony Hopkins as James Herriot and Siegfried Farnon, with Brian Stirner taking the part of Tristan.

[27] After the first rehearsal, Davison met Sinclair, and stated that meeting him "was useful because I'd worried about how to make my Tristan endearing even though he behaved appallingly.

[35] In retirement, Sinclair joined an after-dinner speaking agency,[16][11] and was often invited to give speeches at farmers' functions in the north of England.

[28]: 151  In addition to these talks, he would host informal evenings for American tourist groups visiting "Herriot country",[39] on tours organised by Earl Peel.

[16][5]: 344  He was also due to appear at the centennial annual meeting of the New York State Veterinary Medical Society,[45] but he had a heart attack on 13 December 1988, and died at Leeds General Infirmary,[5]: 344  aged 73 years.

[5][f] His death was an emotional blow to Wight and he would later say that "Brian [Sinclair] may have been a practical joker for most of his life ... but, beneath that hilarious veneer, was a sound and dependable man.