Originally Posted by Matchlock
The depiction that you referred to is part of an altar piece by Hans Baldung Grien called The Adoration of the Magi. According to the New Testament, one of the Magi was Melchior and he indeed is said to have been of African nationality. So this knight represents Melchior.
Don't worry too much about seeing an African wearing a South German early Renaissance suit of armor. In fact, it has nothing to do with the actual historic clothing of African people 500 years ago. The reason why the master painter sort of put him into this armor lies in the fact that the early 16th century Germans who this altar piece was made for wished any work of art to reflect their own contemporary culture, including knightly suits of armor.
When interpreting sources of illustration it is very important to keep in mind the general historic self image of people and both their religious basis and everyday environment at those periods of time.