Arthur Harper (1835–1897) was an Irish-born Yukon River prospector, trader, and explorer, recognized as the first man to enter the Yukon country seeking gold. He mined in California in the 1850s, and British Columbia through the 1860s, before taking off for the Yukon in 1871. He reached Fort Yukon in 1873, and ran a store with Jack McQuesten at the Fortymile River. Harper formed a trading partnership with McQuesten and Captain Al Mayo; their company founded Fort Reliance in 1874 and other posts in the Yukon. Harper was known as the best prospector of the trio, and while he did not achieve major success in his pursuit of gold, he sometimes pointed others to finds. He traded and prospected in Alaska until just before his death.
Arthur Harper was born in County Antrim, present-day Northern Ireland, in 1835. He was educated in local schools, and survived the potato-famine years of the late 1840s. At the age of 20, he left Ireland for California, drawn to prospecting and mining. He searched for gold, but gained mostly experience in prospecting. In the 1860s, he moved on to British Columbia. His prospecting for minerals was mostly devoted to the search for gold.
Harper left British Columbia in 1871, before it became more developed. In 1873, he reached Fort Yukon from the Mackenzie River by way of the Porcupine River, and is credited as the first European to enter the area in the search for gold. He ran a store at Fort Yukon with Jack McQuesten (known as Yukon Jack) beside the Fortymile River. They developed a traders' partnership with Captain Mayo, which the three continued for years. They were known for effectively dealing both with prospectors and the Alaska Native peoples. The three partners each married young Alaska Native women and had families there. In 1875, Harper, McQuesten, and Mayo started a trading post that they called Fort Reliance on the Yukon River, supplying miners up and downriver. It became a point of reference in the area, to the extent that prospectors named creeks and rivers in relation to distance from the post, as in Fortymile River and Sixtymile River. Later Dawson City developed about 6 miles (9.7 km) upriver.