Co-operative Republic of Guyana
Who & why: Guyana becomes independent from Britain on 26 May 1966, initially as a Commonwealth realm under the Queen, then declares itself a co-operative republic in 1970, replacing the monarch with a president as head of state while remaining in the Commonwealth. The Golden Arrowhead flag, designed by American vexillologist Whitney Smith, is adopted at independence in 1966 and has flown unaltered ever since.
What it represents: green for the country's forests and agriculture, gold for its mineral wealth, red for the zeal and dynamism of nation-building, with white and black borders separating and framing the two triangles — one of the very few national flags designed by a professional vexillologist rather than adapted from an older banner.