(

mmm... actually, no, but let's see if anyone manages to guess.
The person I'm referring to (that seems to be, intentionally or not, a sort of prototype for Vincent) is obviously a well-known figure. He was never really massively popular, but had and still has legions of loyal fans (of which I am one). He did have a reputation as a bit of a 'villain'.
He died a few years before the making of Cowboy Bebop.
Similarities:
Firstly, in the look - basically, if Vincent trimmed up his beard a little, and let his moustache grow just a tad more, he'd be a total copy. His general appearance, especially his hair, eyes and nose are basically identical to those of the 'mystery person' (at least during some times in his life. He did cut his hair a bit later on).
Secondly, the movie happens at Halloween, which was the 'mystery man's' favorite day. What's more, pumpkins are prominent in the movie, and Vincent never seems too far from one - just as the 'man in question', who made the pumpkin his trademark.
And last, but not least - the crowning jewel of my hypothesis:
The man's middle name was, yep, you guessed it - Vincent.
***
So, any takers as far as the 'mystery man's' identity? I think this is the movie's main inside joke that noone really caught on to, from what I gather. Or a strange coincidence.