I can find no information about the establishment of the mural, but there is plenty of information about Osmond Gilles, the man.

Osmond Gilles (1788 – 1866), colonial treasurer and pioneer, was born in 1788 in London, the son of Osmond and Hannah Gilles. Of Huguenot descent and well-to-do, he travelled extensively on the Continent before settling in Hamburg as a merchant. There he gained an extensive knowledge of the sheep and wool trade. About 1833 his wife died without issue and Gilles’ thoughts turned to emigration.

By 1836 Gilles was appointed colonial treasurer to South Australia, partly because of his wealth and his loan for the initial expenses. He sailed in the Buffalo with Governor (Sir) John Hindmarsh and reached Holdfast Bay in December 1836. He was one of the few who uniformly supported Hindmarsh, thereby drawing the fire of political opponents and many detractors. The Treasury was generally empty, but Gilles kept it going by personal loans, and carried on his land deals and other business activities as well as bickering with his fellows.

Despite his public brawls and official independence, Gilles retained the favour of Hindmarsh. Governor George Gawler also had a high regard for him but suffered from his neglect and failed to obtain satisfactory statements of accounts. Gawler caused him to resign his offices of treasurer and accountant-general in 1839. Gilles had at least kept the Treasury going; it owed him nearly £12,000, which Gawler repaid.

‘Very irritable’ and with an almost ungovernable temper when excited or provoked, his failure as an official was offset by his success in business. From the beginning his interests were many and varied, including land, stock, money-lending and general trading. His ventures in land were among the most extensive in the province. Profiting by his experience in Germany he was an early importer of sheep. In 1839 he discovered silver-lead on his property at Glen Osmond, which yielded him substantial royalties until the mine was worked out.

Despite his temper, the dominant factors in his private life were his strong religious beliefs and generosity. Soon after arrival he helped the colonial chaplain, Rev. Charles Howard, to drag a handcart under a blazing sun from Holdfast Bay to Adelaide. There they draped a sail over a branch and held the first official service in Adelaide; when Trinity Church was built on the site Gilles was an active trustee and a generous supporter. He gave land and materials for St Saviour's, Glen Osmond, as well as endowing its incumbent. He also gave ready aid to many other churches of various denominations, and to many cultural societies and charitable institutions. Fluent in French and German he took a special interest in immigrant welfare, and in 1852 gave land in Adelaide for a German hospital.

He died at his home, ‘Woodley’, Glen Osmond, on 25 September 1866. As well as tablets in many churches, several streets and districts in Adelaide bear his name.

http://adbonline.anu.edu.au/biogs/A010411b.htm