Royal standard of Thailand
The Royal Standard of Thailand (Thai: ธงมหาราช; BGN/PCGN: Thong Maharat) is the official flag of the King of Thailand. The present form was adopted in 1910 under Vajiravudh (Rama VI), superseding the first Royal Standard created by Mongkut (Rama IV) in 1855.
Source: Wikipedia — Royal standard of Thailand (CC BY-SA 4.0)