Arguably, the single most famous winner of the Tchaikovsky was Van Cliburn in 1958.
This, of course was during the Cold War with the Sovet Union, which was threatening to be "not so cold" with the entire world seemingly on the verge of nuclear apocalypse.
It was Soviet Premier Nikita Kruschev himself who basically "awarded" Van Cliburn the first prize medal, in that the judges sought his permission.
Cliburn a very charismatic figure, of course, was the very essence of humility, diplomacy, and the "international communicator and diplomat of music as a language and 'olive branch' ", and it was correctly surmised that awarding him the first place prize could only be good for Soviet/American relations.
The rest, as they say, is history, and we will likely never again see such fame and a lasting piano career ever created again so fast and almost out of thin air.
It is, of course, merely speculation to say that Cliburn's playing alone without his origins from Texas, USA, without his tall good looks, his humility, grace, etc., and without the perfect timing given the political climate would have resulted in his winning of the most prestigious piano prize at that time.
We simply will never know, but it would seem a bit naive to think Cliburn's extra-musical "assets" both personal and otherwise, had nothing whatsoever to do with his winning.
It really does not matter, however, in that he has exceeded by all measures everything and anything that might have ever been expected of a Tchaikovsky Competition winner, as he remains to this day likely the most famous, inspiring, and influential "pianist/ambassador" in the world with unrivaled accomplishments too numerous and diverse to ennumerate.