Lysander Spooner (1808-1887) was an anarchist considered one of the first American anarchist theorists as well as an early example of somebody holding most of the views making up modern libertarianism.
Spooner was an abolitionist regarding slavery who nonetheless believed that the southern states did have a right to secede. His best known book during his lifetime was The Unconstitutionality of Slavery (1845). He also took part in a failed attempt at freeing John Brown after Brown's arrest in Harper's Ferry, and in 1858 circulated the pamphlet "Plan for the Abolition of Slavery" calling for militant uprisings against slaveholders. However during the American Civil War he came to the conclusion that the United States Constitution had no legal standing and embraced a full-fledged anarchism.
Spooner held Deist religious beliefs.
In 1844, he founded the American Letter Mail Company, a private business directly competing with the government-run postal service for delivery of first class mail. He succeeded in establishing mail delivery through the free market at a lower rate than the government-run post office. The U.S. Congress responded by passing a law outlawing private mail carriers competing with the government's U.S. Postal Service, forcing Spooner out of business by 1851.
His best known book today is No Treason: The Constitution of No Authority, first published in 1867 and kept in print during the last several decades from several publishers due to continuing libertarian interest. This was number 4 in his No Treason series of pamphlets, the name of which came from Spooner's view that Confederate supporters and other rebels were not guilty of "treason" because the government itself had no legitimacy nor any right to prevent secession. No Treason: The Constitution of No Authority makes a case using relentless logic and reason against the legitimacy of the United States Constitution, "social contract" theory, oaths sworn to government entities, etc.
Spooner's book Trial By Jury also remains popular due to his being an early advocate of jury nullification as a defense for runaway slaves.
Murray Rothbard has praised No Treason: The Constitution of No Authority as the "greatest case for anarchist political philosophy ever written", while criticizing Spooner's views on money in his article "The Spooner-Tucker Doctrine" (found in Rothbard's book Egalitarianism as a Revolt Against Nature and Other Essays).