Joshua Abraham Norton (February 4, 1818 – January 8, 1880), known as Emperor Norton, was a resident of San Francisco, California, who in 1859 proclaimed himself "Norton I., Emperor of the United States". In 1863, after Napoleon III invaded Mexico, he took the secondary title of "Protector of Mexico".

Norton was born in England but spent most of his early life in South Africa. Leaving Cape Town, probably in late 1845, he arrived in Boston, via Liverpool, in March 1846 and San Francisco in late 1849. Nothing is known of his whereabouts or occupations in the intervening three-and-a-half years.

For the first few years after arriving in San Francisco, Norton made a successful living as a commodities trader and real estate speculator. However, he was financially ruined following a failed bid to corner the rice market during a shortage prompted by a famine in China. He bought a shipload of Peruvian rice at 12 cents per pound; but more Peruvian ships arrived in port, causing the price to drop sharply to 4 cents. He then lost a protracted lawsuit in which he tried to void his rice contract, and his public prominence faded.

Norton did not disappear from the scene completely. But, he dramatically "reset" his relationship to the world around him in September 1859, when he declared himself Emperor of the United States. Norton had no formal political power; nevertheless, he was treated deferentially in San Francisco, and currency issued in his name was honored in the establishments that he frequented. Some considered him insane or eccentric, but citizens of San Francisco celebrated his imperial presence and his proclamations, such as his order that the United States Congress be dissolved by force and his numerous decrees calling for the construction of a bridge and tunnel crossing San Francisco Bay to connect San Francisco with Oakland. Though Norton received many favors from the city, merchants also capitalized on his notoriety by selling souvenirs bearing his name. "San Francisco lived off the Emperor Norton," Norton's biographer William Drury wrote, "not Norton off San Francisco".On January 8, 1880, Norton collapsed at the corner of California and Dupont (now Grant) streets and died before he could be given medical treatment. According to the San Francisco Chronicle, upwards of 10,000 people lined the streets of San Francisco to pay him homage at his funeral. Norton has been immortalized as the basis of characters in the literature of Mark Twain, Robert Louis Stevenson, Christopher Moore, Morris and René Goscinny, Selma Lagerlöf, G. S. Denning, Neil Gaiman and Charles Bukowski.