(1824 - 1860) was one of the most colorful
and downright wacko
figures in 19th century US history
. He was an adventurer
leader and filibuster
After completing both legal and medical studies in Nashville, he went to California in 1850. Three years later he led an armed invasion of Baja California and proclaimed himself president of the independent republic of Baja California and Sonora. However, he ran out of supplies and had to surrender to the US. He was acquitted of violating neutrality laws in 1854.
One year later, a Nicaraguan revolutionary faction asked Walker for help. Since his ultimate plan still was to unite the republics of Central America under his rule, he led them in the capture of Granada (yes, another invasion). He actually was inaugurated president of Nicaragua in 1856.
Now, taking over Nicaragua was a Big Deal because the country was a key transport link between the Atlantic and Pacific Ocean. Unfortunately Walker's forces were overthrown when Cornelius Vanderbilt became annoyed about losing his industrial and transit resources in Nicaragua. Eventually, Walker had to surrender to the US again when a coalition of Central American states challenged him in 1857.
In 1860, however, Walker had another go at it. He landed in Honduras via the Swan Islands, but was promptly taken prisoner by the British Navy. He was turned over to Honduran authorities and executed in the same year.