The Flag of Thailand shows five horizontal stripes in the colors red, white, blue, white and red. The middle blue strip is twice as wide as the other four. The three colors red-white-blue stand for nation-religion-king, an unofficial motto of Thailand.
The first flag used for Siam was probably a plain red one, first used under King Narai (1656-1688). According to some sources later different symbols were placed on the red ground - a white chakra (the Buddhist wheel), a white elephant inside the chakra, or a white disc with a sun inside.
Officially the first flag was created in 1855 by King Mongkut (Rama IV), showing a white elephant (a royal symbol) on red ground, as the plain colored flag was not distinct enough for international relations.
In 1916 the flag was changed to the current design, but with the middle color being the same red as the outer stripe. The story goes that during a flood King Vajiravudh (Rama VI) saw the flag hanging upside-down, and to prevent this from happening again created a new flag which was symmetrical. In 1917 the middle color was changed to blue, the color for Friday, the day king Rama VI was born.