Xavier Guillaume Mertz (6 October 1882 – 8 January 1913) was a Swiss polar explorer, mountaineer, and skier who took part in the Far Eastern Party, a 1912–1913 component of the Australasian Antarctic Expedition, which claimed his life.

He was initially employed as a ski instructor, but in Antarctica, Mertz instead joined Belgrave Edward Ninnis in the care of the expedition's Greenland huskies.

The cause of Mertz's death has never been firmly established; the commonly purported theory is hypervitaminosis A—an excessive intake of vitamin A—from consuming the livers of the Huskies.

With the aim of working in the family business, which manufactured textile machinery, Mertz attended the University of Bern, where he studied patent law.

"[5] While Mawson was intending to recruit only British subjects (chiefly Australians and New Zealanders), Mertz's qualifications prompted him to make an exception, and hire the Swiss as a ski instructor.

Because the conditions—constant, strong winds and an excessive slope by the hut—prevented Mertz from conducting skiing lessons as regularly as intended, he focussed instead on helping Ninnis to care for the dogs.

[19] Mertz and Ninnis were assigned to Mawson's own party, which would use the dogs to push quickly to the east of the expedition's base in Commonwealth Bay, towards Victoria Land.

[20] The party departed Cape Denison on 10 November, heading first to Aladdin's Cave, and from there south-east towards a massive glacier encountered by Aurora on the outward journey.

As Mertz skied ahead, singing songs from his student days, Ninnis, the largest sledge and the strongest dog team were lost when they broke through the snow lid of a crevasse.

[28] They immediately turned back west, gradually using the six remaining dogs to supplement their food supply; they ate all parts of the animals, including their livers.

[29] They initially made good progress, but as they cleared the largest glacier Mertz began to feel ill; he had lost his waterproof overpants on Ninnis' sledge, and in the cold his wet clothes were unable to dry.

[32] On 8 January, with the pair about 100 miles (160 km) from the hut, Mawson recorded: He [Mertz] is very weak, becomes more and more delirious, rarely being able to speak coherently.

[33][34]Mawson buried Mertz in his sleeping bag under rough-hewn blocks of snow, along with the remaining photographic plates and an explanatory note.

[36][37] In November 1913, a month before the Aurora returned for the final time, Mawson and the six men remaining at Cape Denison erected a memorial cross for Mertz and Ninnis on Azimuth Hill to the north-west of the main hut.

[38][better source needed] The cross, constructed from pieces of a broken radio mast, was accompanied by a plaque cut from wood from Mertz's bunk.

[47] Phillip Law, former director of Australian National Antarctic Research Expeditions, believed cold exposure could account for Mertz's symptoms.