James King of William (January 28, 1822 – May 20, 1856) was a crusading San Francisco, California, newspaper editor whose assassination by James P. Casey, a member of the San Francisco Board of Supervisors, in 1856 resulted in the establishment of the second San Francisco Vigilance Committee and changed the politics of the city. King was among the first newspapermen to be honored by the California Journalism Hall of Fame.

James King was born January 28, 1822, in the Georgetown district of Washington, D.C., the seventh and youngest son of William King, a native of Ireland. When he was age sixteen, he began to style himself "James King of William", to distinguish himself from other James Kings in the area.

It was said that "He was an eager student, acquired a fair knowledge of Latin and English literature, and learned to speak French, Spanish and some German." He was married in 1843 to Charlotte M. Libbey of Georgetown, and they had six children. In 1848 he departed for the Pacific Coast "to improve his prospects and establish a new home for his family," whom he left behind until 1851, when they joined him in California.

King left home at the age of fifteen and worked first as a clerk in Pittsburgh, Pennsylvania, then in St. Joseph, Missouri, whence illness forced him to return to Georgetown in 1838, where he was a post office clerk. Soon he became a political journalist on Kendall's Expositor, a Democratic-leaning newspaper issued in Georgetown, and on the Washington Daily Globe, where he was also advertising manager. He was later a bookkeeper for the mercantile or financial firm of Corcoran & Riggs, until 1848.

Influenced by the letters of a brother, whose name was variously reported as Thomas, who assertedly wrote from Oregon, or as an elder brother, Henry, who wrote from California, King on May 24, 1848, sailed for Cartagena, Colombia, and made his way to the Pacific Ocean at the isthmus of Panama, where he was disappointed to find there was no ship on the west coast to take him north. He journeyed to Callao, Peru, and then Valparaiso, Chile, where, having heard about the gold strike in California, he purchased a stock of goods and hired nine men to sail with him to California aboard the Undine. After arrival on November 10, most of the men deserted him, but with the others he gathered enough gold near Hangtown (now Placerville), to make a "considerable financial success" of the placer mining venture. Soon he began trading gold coins or offering bills of trade for the miner's gold dust.

Leaving the California gold country, King joined the mercantile house of Hensley, Reading & Company in Sacramento for a short time, but in July 1849 he went back to Washington and arranged for a loan from the financial firm of Corcoran & Riggs; he returned on December 5, 1849, and opened his own bank on Montgomery Street. It was in this year that he first began issuing private gold ingots.

At first the bank was successful, with King being regarded as one of the wealthiest men on the West Coast, but his agent in Sonoma County "used large sums of money, intended for purchasing gold, to invest in the stock of the bankruptcy-bound Tuolumne Hydraulic Association." The financial loss left King penniless by early 1850, and while paying off his debts he worked for Adams & Company. He next became a partner with bankers Samuel J. Hensley and Robert D. Merrill in April 1850 and was their agent for two months. He went back to Washington briefly, then returned to San Francisco in January 1851 on the steamer Tennessee, along with Augustus Humbert, who had been appointed to be U.S. assayer in San Francisco. In that year King established another company, and it was there that his firm struck $20 gold ingots.

Coin historian Donald H. Kagin has written that in March 1851, "the most notorious chapter in private gold coinage occurred", when King sent $180 in face value of coins minted by a number of entrepreneurs to Humbert, who reported after assaying them that the samples were worth 1.8 percent to 3 percent under market value. King sent these results and related correspondence to every major newspaper, and the resulting public outcry impelled the California Legislature to effectively end the use of private coins in an act dated April 15, 1851. Kagin said that King therefore "may have started" the California economic recession of 1850–51, "whose effects he certainly accentuated." However, Kagin is incorrect. The Act was passed into law on April 21, 1851.