The flag of Thailand is a horizontal tricolor flag with the colors of red, blue and white. The top and bottom thirds of the flag consist of two equal horizontal red and white bands. The middle third of the flag is a dark blue horizontal band. The design was officially adopted in September of 1917 by authorization from Rama VI. The colors stand for nation, religion and king, which is considered an unofficial motto of the country. Red stands for the land and people, while white represents religion and blue represents the king. Blue was a color that represented Rama VI at the time it was adopted. It is also notable that at the time, Thailand was declaring war on Germany along with Britain, America and France. The color choice was either very coincidental or purposeful to represent solidarity with those allies.
A variant flag of Thailand uses the same color combination and layout as the official flag, but also includes an elephant in the middle with a cap and blanket. That flag was also chosen and designed by King Vajiravudh (Rama VI). This flag is used by the Thai Royal Navy.
Previous flags of Thailand or Siam have generally been some type of red flag. The first known flag was a simple red rectangle between 1700 and 1790, then between 1790 and 1855 as a civil ensign. For a period between 1790 and 1820, a white chakra was added to the center of the red flag to represent the Chakri Dynasty. Another change between 1820 and 1855 added an elephant to the middle of the chakra. Between 1855 and 1893, the flag was a red flag with an elephant taking up much of the middle of the flag. It became the civil ensign between 1893 and 1916, as the new state one replaced it. That new flag added a cap and blanket to the elephant, as well as put it on a dais. This flag was the state flag from 1893 to 1898, then again between 1912 and 1917.
In 1917, the modern Thailand flag was adopted, though the civil ensign became a red and white striped flag laid out like the state flag. After 1917, the modern flag became the flag for national, state and civil purposes.