The San Francisco Herald, or San Francisco Daily Herald, was a newspaper that was published from 1850 to 1862 in San Francisco, California. The paper stood out aggressively against crime and corruption associated with the California Gold Rush. The editors fought several duels with men whom they had offended. In 1856 the paper attacked the Vigilance Committee, which was taking the law into its own hands. Supporters of the committee withdrew their subscriptions and advertising, almost forcing the newspaper to close. However, the newspaper continued to be published with smaller circulation until 1862.

William Walker was an American physician, lawyer, journalist, and mercenary. In the era of the expansion of the United States, driven by the doctrine of "manifest destiny", Walker organized unauthorized military expeditions into Mexico and Central America with the intention of establishing slaveholding colonies. Such an enterprise was known at the time as "filibustering".