Frederick Albert Cook (June 10, 1865 – August 5, 1940) was an American explorer, medical doctor and ethnographer, who is most known for allegedly being the first to reach the North Pole on April 21, 1908. A competing claim was made a year later by Robert Peary, though both men's accounts have since been fiercely disputed; in December 1909, after reviewing Cook's limited records, a commission of the University of Copenhagen ruled his claim unproven. Nonetheless, in 1911, Cook published a memoir of the expedition in which he maintained the veracity of his assertions. In addition, he also claimed to have been the first person to reach the summit of Denali (also known as Mount McKinley), the highest mountain in North America, a claim which has since been similarly discredited. Though he may not have achieved either Denali or the North Pole, his was the first and only expedition where a United States national discovered an Arctic island in North America, Meighen Island.

Cook also remains well-known for his participation on the Belgian Antarctic Expedition (1897–1899) where, as the sole doctor on board, he is widely credited with saving most of the crew from death through his medical perception.^{[additional citation(s) needed]}

Cook was born in Hortonville, New York, in Sullivan County. (His birthplace is sometimes listed as Callicoon or Delaware, both also in Sullivan County.) His parents, Theodor and Magdalena Koch, were recent German immigrants who adopted an anglicized version of their surname. He attended local schools before college. After graduating from Columbia University, he studied medicine at what is today NYU's Grossman School of Medicine, receiving his doctorate in 1890.

Cook married Libby Forbes in 1889. She died two years later. In 1902, on his 37th birthday, he married Marie Fidele Hunt. They had two daughters together. They divorced in 1923.

Cook was the surgeon on Robert Peary's Arctic expedition of 1891–1892, and on the Belgian Antarctic Expedition of 1897–1899. He contributed to saving the lives of its crew members when their ship – the Belgica – was ice-bound during the winter, as they had not prepared for such an event. It became the first expedition to winter in the Antarctic region. To prevent scurvy, Cook went hunting to keep the crew supplied with fresh meat. One of the crew members was Roald Amundsen, who credited Cook with his survival in his diary of the expedition.

In 1897, Cook twice visited Tierra del Fuego, where he met the English missionary Thomas Bridges. They studied the Selkʼnam and Yahgan peoples, with whom Bridges had worked for two decades. During this time, Bridges had prepared a manuscript on their language's grammar and a dictionary of more than 30,000 words. Several years later, Cook tried to publish the dictionary as his own.

In 1903, Cook led an expedition to Denali, during which he circumnavigated the range. He made a second journey in 1906, after which he claimed to have achieved the first summit of its peak with one other expedition crew member. Other members, including Belmore Browne, whom Cook had left on the lower mountain, immediately but privately expressed doubt. Cook's claims were not publicly challenged until 1909 when the dispute with Peary over the North Pole claim erupted, with Peary's supporters claiming Cook's Denali ascent was also fraudulent.

Unlike Harry Karstens and Hudson Stuck in 1913, Cook had not taken photographs from atop Denali. His alleged photo of the summit was found to have been taken on a small outcrop on a ridge beside the Ruth Glacier, 19 miles (31 km) away.