I don't know who this photo is of, although I presume it is of one of the kings. since it is within the era of photography, my guess would be one of the Ramas, and clearly youthful. King Rama V is often depicted, but the photos I've seen of him are usually well into middle age. This one is an enigma. The photo is strongly contrasting light and shadow, while his sash has been artificially coloured.