The origin of the flag of Saudi Arabia

   The "base flag" of Saudi Arabia, the shahada or profession of faith ("There is no god but Allah and Muhammad is his Prophet") on solid green was an old flag, connected to the Wahhabi reformist movement of the late 18th century, with whose religious drive the as-Saud family first rose to power.
The sword was added in 1902, when Abdulaziz ibn Abdulrahman as-Saud ("Ibn Saud" to the British) established himself as King of the Nejd. (The King of the Hejaz, Hussein, used the Arab Revolt Flag).

In 1925, Abdulaziz established himself as King of the Nejd and Hejaz, with unknown flag alterations.
 

"Sharif Hussein designed the flag of
the Arab Revolt on June 1916

When the Kingdom of Saudi Arabia was established in 1932, the earlier Nejdi flag continued, though variants are shown with two swords, with a white stripe toward the hoist, etc.	Today's Royal Flag
Today's Flag