The Siamese Fireback(Lophura diardi) also sometimes refereed to as Diards Fireback is the National Bird of Thailand.
The bird is a fairly large pheasant with the male and female exhibiting different plumage. It is a secretive forest dwelling bird found in Thailand and Indochina.
The Siamese Fireback is so named because of the yellow patch on the back towards the rump of the male bird. Often this is only visible when the bird is displaying.
The birds scientific name Lophura diardi is said to have been given by a nephew of the Emperor Napoleon, Charles Lucien Bonaparte, who first described the bird.
It commemorates the French naturalist Pierre-Médard Diard.
I can find no information of how the Siamese Fireback became the National bird of Thailand. Given that it is not a Thai endemic perhaps it is simply because the common English name contains the old name for Thailand(Siam).
In June 2019 I was fortunate enough to observe both male and female Siamese Firebacks at Nam Nao National Park, Phetchabun Thailand.
Once this species was considered at risk but now, perhaps because of captive breeding and release by the Thai Department of National Parks, the birds can be seen in several Thai National Parks including Khao Yai.