All descriptions of BunianTu 步辇图 say it's LuDongZan, the Prime Minister of Tibetan.
But I have to doubt on it.

1 Where's the evidence or ancient record of this saying?

2 His clothes is a typical centra asia style like Uighur , is it a Tibetan style?

3 His face is also a central asia style with brown light beard, but Tibetans often have no beard.

4 The man in the picture is only a small messenger, could it be the Prime Minister of
Tibetan Empire then?

here's the picture.

This is the full picture of the painting 《步辇图》 (Bu Nian Tu) depicting a scene around AD 640 of Tibetan envoys meeting Emperor Taizong of Tang dynasty. "Bu Nian 步辇" is the term used for describing the 'sedan chair' which the Emperor is sitting on. The painting was done by Tang painter Yan Liben (阎立本).

According to most interpretation by chinese, the figures are as follow from left to right: Translator, Lu Dongstan 禄东赞 (Tibetan envoy), Tang official, Emperor Taizong (Li Shimin).

My question is why it's Tibetan Prime Minister LuDongZan,
where's the evidence?
If no evidence, we can say he is a messenger from Uighur or some other country as well,
couldn't we?
Evidence and origin!

The above is a typical Chinese explanation of what the painting depicts, from http://www.tibetcul.com/renwu/ls/gjms/200612/2132.html

It looks like a big part of the problem is how we know that the painting is showing the moment when mGarstongrtsanyulzung (his Tibetan name; see http://zh.wikipedia.org/wiki/%E7%A6%84%E4%B8%9C%E8%B5%9E ) is proposing the marriage alliance to Li Shimin. This is the traditional interpretation of the painting, but there is no textual record of Yan Liben's work to prove it.

Another related problem is whether the painting is even an authentic Tang work. Chen Peiqiu, a prominent Chinese art historian and critic, concluded in 2002 that it is a forgery:

http://www.zgyspp.com/Article/y6/y53/200610/3162.htm

Good observation. I can see strong Sogdian influence in this middle man's costume. However, I don't see any reason a Tibetan diplomat could not wear a Sogdian style suit. In fact, in Tang era, the Sogdian fashion was favoured by all Middle Asian nations; you can even see the clothes on two Tang scholars aside were not totally in Hanfu style.

Yun,
So if there'no reliable evidence of this painting's origin, we can sonsider the traditional saying
is a fake explanation, no matter if it's a work of Tang.



Of course, he could wear whatever he liked, but could he wear in alien style
in such a formal official occasion as a prime minister and an ambassador?

And Tibet at that time have nothing to do with Turkestan nations, see mordern Tibetans
and the statue of Songzanganbu, Tibet have never been influenced by Turkic culture, even
they ever ruled eastern Turkestan (maybe for a centry) later.
Furthermore, most Tibetans have no beard.

The two Tang officials reveals the different races of then North Chinese(Turkic/Hunnic, the official with heavy beard in red) and South Chinese(real Chinese, the interpreter without beard in white)

So I think he's only a messenger from some country of Western Region.
That's much more reasonable than the traditional explanation.

Tubo had a more close relation to Tujue/Uigur than to Tang then.