William Edward Petty Hartnell, later known by his Spanish name Don Guillermo Arnel, was a merchant, schoolmaster, and government official in California. He arrived in California in 1822 as a trader, where he married into the prominent Guerra family of California and became a Mexican citizen. He held several public roles during the Mexican era and after the American Conquest of California, notably serving as the official translator at the Monterey Constitutional Convention.

The California hide trade was a trading system of various products based in cities along the California coastline, operating from the early 1820s to the mid-1840s.