He is principally known for his study of the Hindustani language, which led to it being adopted as the lingua franca of northern India (including present-day Pakistan) by British colonists and indigenous people.

[10] He marched with the company's Bengal Army to Fatehgarh, and during this journey he noted the extent to which the Hindustani language could be understood in different parts of the country.

In Ghazipur, to help finance his work, he also engaged in the production of indigo, sugar and opium – an enterprise which was initially successful but eventually failed.

[12] In Northern India, the Hindustani language developed from the need of the new migrants of Persian and Turkish origin to communicate with people in Delhi and the surrounding regions.

The local populace spoke Dehlavi dialect, one of the Hindi languages, which supplied the basic vocabulary and grammar but also absorbed a lot of words from Persian to form Hindustani.

[1][12][13] On Gilchrist's suggestion, the Governor-General, the Marquess of Wellesley, and the East India Company decided to set up a training institution for its recruits in Calcutta.

Gilchrist served as the first principal of the college until 1804, and through the personal patronage of Wellesley received a generous salary of 1500 rupees a month, or about £1800 per year (about £180,000 in present-day terms).

He gathered around him writers from all over India who were able to produce a simple Urdu style that was "intelligible to British officers and merchants who had no use for poetry".

"[17] Another view was that of George Abraham Grierson, an Irish linguist and civil servant, who said that the standard or pure Hindi which contemporary Indians use is "an artificial dialect the mother tongue of no native-born Indian, a newly invented speech, that wonderful hybrid known to Europeans as Hindi and invented by them.

[9] Gilchrist never went to Australia, but as Sydney subsequently developed, the value of this holding (now part of the suburb named Balmain) rose substantially.

"[10] In 1806, when the East India College was established at Haileybury, Hertfordshire, its original plan called only for the teaching of Arabic and Persian.

He then moved to London in 1817 and the following year was appointed as lecturer in oriental languages for the East India Company, a position he held until 1825.

However, after this employment ceased, he controversially continued to give lectures without payment, as a vehicle to promote the sale of his works as textbooks.

He settled in Paris almost permanently from 1831 onwards, obtaining a French passport for himself, his wife and two servants, and resided in the Rue Matignon.

[18] Gilchrist left a considerable fortune, which included property and investments in London and Edinburgh, as well as the Balmain estate in Australia.

In his will, he appointed the Member of Parliament, Joseph Hume, to be his principal executor, and instructed that his assets be sold and the proceeds held in a charitable trust.

The residual income he instructed to be used "for the benefit and advancement and propagation of education and learning in every part of the world as far as circumstances will permit.

The case, known as Whicker v Hume, was complex and considered several issues: The case dragged on for many years and eventually went as far as the House of Lords, which handed down its final judgement upholding the validity of the will in July 1858, over 17 years after Gilchrist's death and after which time several of the parties, including both Whicker and Hume, had themselves died.

Inevitably, these views made him enemies, and together with the collapse of his banking business, it led him to forsake his native city for the rest of his life – returning only occasionally for brief visits to his mother.

There are no likenesses of him in his younger days, but as an old man Chambers' Biographical Dictionary describes him as "his bushy head and whiskers were as white as the Himalayan snow, and in such contrast to the active expressive face which beamed from the centre of the mass, that he was likened to a royal Bengal tiger – a resemblance of which he was even proud."