It does depend what you mean by ‘historical’? If you mean the furthest back in time then I would suggest you look into Septimus Severus who was Roman Emperor from and 193 to 211 which made him the ruler of England. He actually died in the city of York. Of course there were plenty of black people in England even before Septimus but he is arguably the one we know most about. Pretty amazing that England was governed by a black man almost two thousand years ago!