Which Thai king standardized Siam's modern tricolor flag in 1917?

King Vajiravudh standardized Siam’s modern tricolor flag in 1917. He was Rama VI, who reigned from 1910 to 1925, and the flag was officially adopted on September 28, 1917.

The Trairanga has five horizontal stripes: red, white, blue, white, and red. Its central blue stripe is twice as wide as each of the other four. Red, white, and blue are commonly associated with the nation and people, religion, and monarchy, respectively.

The flag replaced earlier designs featuring a white elephant on a red field. A red-and-white striped version appeared first in 1916, before Vajiravudh changed the central stripe to dark blue in 1917. The blue was linked to his auspicious birth color and is also often connected with Thailand’s World War I allies.

A common mix-up is attributing the flag to King Chulalongkorn, who preceded Vajiravudh and introduced important earlier reforms and flag changes. The present design remains Thailand’s national flag.