"The infantry are quite cut up – not over their terrible losses, but because of one man, Simpson Kirkpatrick I think his name is.  He was known everywhere as “Murph. And his Donk”.  At the Landing he commandeered a donkey and ever since has been coming and going from the distant firing-line to the beach with wounded men.  He worked day and night, plodding along unscathed under fire till all thought he must be protected by supernatural means.  His colonel long ago told him to carry on all on his own; to do whatever he liked and go wherever he liked.  He has been a little army of mercy all on his own.  Yesterday morning, I think it was, he went up the valley and stopped by the Water Guard where he generally had breakfast.  It wasn’t ready so he went on, calling, “Never mind, give me a good dinner when I come back.”

He never came back.  Coming along the valley holding two wounded men to the donkey he was shot through the heart.  Both wounded men were wounded again."

Ion IDRIESS, The Desert Column.  Chapter 2 – Shrapnel Gully, Gallipoli – 22 May 1915.

"One bearer there was whose name has become a tradition in Australia.  A number of donkeys with Greek drivers had been landed on April 25th for water-carrying.  The Greeks were soon deported, and after the first days the donkeys ceased carrying and fed idly in the gullies, till they gradually disappeared.  Private Simpson, of the 3rd Australian Field Ambulance, was seized with the idea that one of these might be useful for moving men wounded in the leg.  On the night of April 25th he annexed a donkey, and each day, and half of every night, he worked continuously between the head of Monash Valley and the Beach, his donkey carrying a brassard round its forehead and a wounded man on its back.  Simpson escaped death so many times that he was completely fatalistic; the deadly sniping down the valley and the most furious shrapnel fire never stopped him.  The colonel of his ambulance, recognising the value of his work, allowed him to carry on as a completely separate unit.  He camped with his donkey at the Indian mule-camp, and had only to report once a day at the field ambulance.  Presently he annexed a second donkey.  On May 19th he went up the valley past the water-guard, where he generally had his breakfast, but it was not ready.  "Never mind", he called.  "Get me a good dinner when I come back".

He never came back.  With two patients he was coming down the creek-bed, when he was hit through the heart, both the wounded men being wounded again.  He had carried many scores of men down the valley, and had saved many lives at the cost of his own."

BEAN, C E W, The Official History of Australia in the war of 1914-1918, The Story of Anzac, volume 1, 11th edition, pages 553-554 (source 1)