Leslie Henry Charles Clark was the second son of Samuel Clark, a railway employee, and his wife Charlotte.   He enlisted at age 18 years 6 months on 8 April 1916 at Melbourne, making his birth date around November, 1897. His brother, Percy Victor Clark, enlisted the same year, on 17 April, aged 22 years and three months, so it would seem he was following on from his younger brother.  Both young men had served, and continued to serve, in the Senior Cadets, Leslie for four years prior to enlistment. They had both attended Brighton St. State School in Richmond. Leslie was working as a Postal Assistant and living at home, at 'Waratah', 132 Powlett Street, East Melbourne. Percy was an Electric Wireman, also living at home with their parents.

On 8 April, Leslie was sent to begin his military training at Royal Park, Melbourne with C Company Depot Battalion. He remained there until 31 May, when he was moved to B Company, 24th Battalion, thne on 23 June, to the Signal School, where he was taken on strength with the 4th Reinforcements 1st Wireless Squad at Broadmeadows as a Sapper.

After Broadmeadows, he left for active service as a wireless operator, embarking on RS Mooltan on 22 August, 1916, and disembarking at Basra on 11 October, 1916. His service record is very sketchy, but a letter from him (with photo) was published in the Richmond Guardian of 10 February, 1917. Headed 'Balmain Boy in Garden of Eden' by the Editor and 'Somewhere in Mesopotamia' by Leslie, he paints a picture of an easy war: 

Just a line to let you know that I am in the best of health ... We expect to arrive at our destination tomorrow. We left Margil, where I received letters and papers, and started off on the track on the 18th and reached a place called Ghermat Ali, where we camped for the night ... Next day we reached Nahrun and had a swim in the Shatt-el-Arab. We marched into Shaifa and a large town called Kunrna, at the mouth of the Tigris and Euphrates and, incidentally, passed over the ground where the Garden of Eden is supposed to have been. Next pushing on to Sakhrasha, we discovered an Arab canteen which we tickled up to some tune.

 From there, they headed deeper into Mesopotamia (present day Iraq), were taken by barges up the river Nigris, visited the tomb of the prophet Ezra, remained well fed, because, according to Sapper Clark, they had taken plenty of canned fruit with them. It was not all idyllic, however:

... we are beginning to catch the wet weather now and the place is a dead rink (sic)  for Broadmeadows - no grass to be seen, the road about three inches  thick with mud. We have had an experiencese of being bombed by aerolplane. It was back at an Arab village. Fritz was sighted flying high. The monitor and land batteries peppered him in fine style, but he was flying too high and fast and he dropped his few bombs near the camp but they did no damage.

Leslie Clark came through the war unscathed, except for a brief stay in hospital in May, 1918. He began the journey home on 26 February, 1919, embarking for Bombay on SS Northbrook. he then went by train to Deulali, and embarked on SS Janus for Melbourne on 21 March, 1919, from Calcutta. He disembarked on 19 April, 1919, and was discharged from the army on 27 May.

What he did after the war, and where he lived, is a mystery. He does not appear on the Electoral Rolls at all, and cannot be found in the Birth, Marriage or Death indexes on Ancestry.com.au. It would seem that he was in East Melbourne in 1926. A letter, dated 22 December, 1926,  from the Curator of Parks and Gardens at the Melbourne City Council returned a British War Medal found in the Fitzroy Gardens. on 31 December, there was a response, identifying the medal as belonging to L. H. C. Clark, and promising to return it to him. Other than that, there is no further information.