Friedrich Wilhelm Ludwig Leichhardt (October 23, 1813 - 1848?) was a Prussian explorer and naturalist. He was born in Trebatsch, Prussia (now Brandenburg, Germany).
Between 1831 and 1836 Leichhardt studied philosophy, language, and natural sciences at the Universities of Berlin and Göttingen but never received a university degree. He moved to England in 1837 where he continued his study of natural sciences at various places, including the British Museum, London and the Jardin des Plantes, Paris, and undertook field work in several European countries including France, Italy and Switzerland.
In 1842 Leichhardt moved to Sydney, Australia where he led three major expeditions. The first started on October 1, 1844 from Jimbour on the Darling Downs and ended after a nearly 4800 km overland journey in Port Essington on December 17, 1845. The "Journal of an Overland Expedition in Australia, from Moreton Bay to Port Essington, a Distance of Upwards of 3000 Miles, During the Years 1844-1845" by Leichhardt describes this expedition.
The second expedition, starting in December 1846, was supposed to take him from the Darling Downs to the West coast of Australia and ultimately to the Swan River and Perth. After covering only 800 km the expedition team was forced to return in June 1847 due to heavy rain, malarial fever and famine. After recovering, Leichhardt spent 6 weeks in 1847 to examine the course of the Condamine River and the country between the route of another expedition led by Mitchell in 1846 and his own route, covering nearly 1000 km.
In March 1848 he again set out from the Condamine River to reach the Swan River. He was last seen on April 3, 1848 at McPherson's Station, Coogoon on the Darling Downs. His disappearance after moving inland, although investigated by many, remains a mystery. The authentication of Leichhardts Rifle nameplate (an inscribed flattened brass nail) at Sturt Creek WA (news 24/11/06) may shed more light on that mystery.
The Inner Western Sydney suburb of Leichhardt and the surrounding Municipality of Leichhardt are named for him, as is the Leichhardt Highway. Leichhardt's last expedition was the inspiration for Patrick White's novel Voss.
Four years after Leichhardt's disappearance, the Government of New South Wales sent out a search expedition under Hovendon Heley. The expedition found nothing but a single campsite with a tree marked "L" over "XVA". In 1858, another search expedition was sent out, this time under Augustus Gregory. This expedition found only a couple of trees marked "L". In 1865, Duncan McIntyre was shown a tree marked "L" on the Flinders River near the Gulf of Carpentaria. This mark was almost certainly made by William Landsborough; or if it was made by Leichhardt then it would have been during his 1844 journey to Port Essington. However, McIntyre reported to Melbourne that he had found traces of Leichhardt, and was subsequently appointed leader of a search expedition. This expedition was a complete failure, not even reaching the search area. In 1869, the Government of Western Australia heard rumours of a place where the remains of horses and men killed by Indigenous Australians could be seen. A search expedition was sent out under John Forrest, but nothing was found, and it was decided that the story might refer to the bones of horses left for dead at Poison Rock during Robert Austin's expedition of 1854.
The mystery of Leichhardt's fate remained in the minds of explorers for many years: during David Carnegie's 1896 expedition through the Gibson and Great Sandy Deserts, he encountered some Indigenous Australians who had amongst their possessions an iron tent peg, the lid of a tin matchbox, and part of the ironwork of a saddle. Carnegie speculated that these were originally from Leichhardt's expedition.
In 2006 Australian historians authenticated a tiny brass plate bearing Leichhardt's name, originally discovered by an Aboriginal stockman near Sturt Creek on the Western Australia-Northern Territory border about 1900.