The Public Medievalist’s current series on Race, Racism and the Middle Ages, by Adam Simmons, is definitely worth exploring:
… were sub-Saharan African people present in medieval Europe? Despite their glaring absence from many histories, both popular and academic, they were. They came as traders, as explorers, as warriors, or—for those we only know by the archaeological record—for many reasons that we will never know. One in particular came as a king.
Click on the link above for more.