... No, I lie. The party leader of my longest-running campaign was a remarkably honourable and almost knightly fellow, when I stop to think about it; rather an impressive feat, seeing as the gentleman in question was a thief. (he would be the unfortunate soul who was dressed in the fighter-mage's gown at the temple-warming party.)
Nonetheless -- and this is despite a fair few games having all the themes and trappings and even with some players being disappointed without them -- no one has ever actually played the archetype. Or even make small noises towards considering the idea.
Now, I myself am quite partial to paladins if not to all of the sometimes very culturally-specific trappings of the stereotypical knightly behaviour; many of the characters I enjoying reading about, making wander about in a video game or that I've written arguably have "lawful (good)" traits or would fall right in the middle. But I haven't played a paladin either, in the rare few times I've managed to be a player ...
But in hindsight, I do find it likely that if I had tried to run a character along those lines I would have been disappointed -- the archetype, unless juggled veeeery~ carefully, doesn't really lend itself well to the behaviour of the "typical" adventuring party. And bending the intentions and fun of my fellow players as a group just so I could have my shining knight, frankly, just wouldn't have been very knightly.