The most common assumptions I have heard is that Baron Cohen is playing a black man, a white man trying to be black, or an Asian man trying to be black. Among the rank outsiders are that he is Turkish, Greek and Middle Eastern. Asian guys trying to be cool like black guys. Those who have not read profiles of Baron Cohen are equally uncertain of the actor's own racial identity. He covers his hair with a Tommy Hilfiger head band and often hides his face behind ringed fingers.
Guesses range from mixed-race and Asian to caucasian and any number of variations in between.
Herein lies an understandable source of tension. We do not exactly know everything that we are laughing at. Ali G works on so many different levels that you can have two different people watching the same video and laughing at completely different things. One might be finding it funny the way this white comedian is poking fun at white people who overdo their impression of black youth culture. This is the most commonly held view, which casts Ali G as an exaggerated version of Tim Westwood, the popular, white Radio1 DJ who has feigned a black street accent for his hip hop slot.