The Antarctic Peninsula was discovered and frequented by sealers and whalers long before any officially documented discovery. It was thought to be part of the continent of Antarctica, and then to be a grouping of islands. The northwest corner of the region was mapped in 1820 by the British navigator James Bransfield, and John Rymill's expedition from 1934-37 proved its status as a peninsula. It was fist named the Palmer Peninsula for U.S. captain Nathaniel Palmer who also explored the region in 1820.
Britain claimed the peninsula in 1840 and dubbed it Graham Land and Trinity Peninsula. In 1940, Argentina claimed it for its own and called it San Martin Land. Barely two years later, Chile threw in its claim and named it O'Higgins Land.
Finally, in 1964, an international agreement renamed the region the Antarctic Peninsula. However, each country with a previous claim still uses its own name locally. It is now the site of several research stations run by different countries.