The Bible says that after the birth of Christ, wise men (magi) from the East came to worship him. They told King Herod of the child, thus unwittingly causing the Massacre of the Innocents (Matthew 2).
The wise men are frequently portrayed as kings. Painters therefore had considerable scope for depicting detailed finery. One of them (Balthazar) is often shown as black. They brought symbolic gifts: gold for a king; frankincense for a priest; and myrrh for suffering and death.