William Charles Achi was born December 16, 1858, at Kohala, Hawaii, to Lum and Kinilau (Lualoa) Achi, he was the great great grandson of Puou, one of the warriors of King Kamehameha I.

He was educated at Hilo Boarding School, the Lahainaluna Seminary, Maui, and at Oahu College in Honolulu in 1882.

[1] Achi read law in the office of William Richards Castle in Honolulu, and was admitted to the courts of Hawaii in February, 1887.

[1] Achi married Maria (Isabella) Alapai on June 15, 1883[3] but they divorced.

[4] Their son, William Charles Achi Jr. (1889–1947), became an attorney, and was eventually appointed by Woodrow Wilson to be a territorial judge.