Oahu has long been known as "The Gathering Place" because it is the most densely populated of the Hawaiian Islands (home to over two-thirds of the population of the state of Hawaii) despite being only the third largest island.

Ancient Hawaiian tradition attributes the name's origin in the legend of Hawai'iloa, the Polynesian navigator credited with discovery of the Hawaiian Islands. The story relates that he named the islands after his children: Maui (son), Kauai (son), and Oahu (daughter) who settled on the islands that bear their names.

The island is composed of two separate shield volcanoes: the Wai'anae and Ko'olau Ranges, with a broad valley or saddle (the central Oahu Plain) in between.

From 1939 to 1940, Maunawili Ranch on the island of Oahu saw 331 straight days with measurable rain, which dwarfs the mainland USA record of 79 days set near Otis, Oregon, in the winter of 1997-98.

Kamehameha III moved his capital from Maui to Oahu in 1845. 'Iolani Palace, located in the capitol district of downtown Honolulu, is still standing, and is the only royal palace on American soil. After the monarchy was overthrown in 1893, the building was used as the capitol building for the Provisional Government, Republic, Territory, and State of Hawaii until 1969.

In 1783, Kahekili II, who was named after the Hawaiian god of thunder, conquered Oahu and deposed the reigning family. He made his son, Kalanikūpule, king of Oahu, turning Oahu into a puppet state.

Although Oahu was sighted by the crew of HMS Resolution on January 19, 1778, during Captain James Cook's third Pacific expedition, it wasn't actually visited by Europeans until February 28, 1779, when Captain Charles Clerke stepped ashore at Waimea Bay. Clerke had taken command of HMS Resolution after Cook was killed at Kealakekua Bay on the Big Island.

The Imperial Japanese Navy's attack on Pearl Harbor, Oahu on the morning of December 7, 1941 resulted in the deaths of 2,335 American servicemen and 68 civilians. The attack was meant to prevent the United States from interfering with Japan's planned military actions in the Pacific theater, but it led to America's formal entry into World War II the very next day.

The origin of the shaka sign, sometimes known as "hang loose", can be traced back to Hamana Kalili of Oahu, who lost the three middle fingers of his right hand while working at the Kahuku Sugar Mill. Kalili was then shifted to guarding the sugar train, and his all-clear wave of thumb and pinkie is said to have evolved into the shaka as children imitated the gesture. Today, Hawaiians use the shaka to convey the "Aloha Spirit", a concept of friendship, understanding, compassion, and solidarity.

Barack Obama was born on August 4, 1961, at Kapiolani Medical Center for Women and Children on Oahu, making him the only U.S. president born outside the contiguous 48 states.