The Three Kings (also known as the Magi) followed the star from the East which directed them to the stable where the newborn Christ lay. Saint Matthew's Gospel (Matthew 2: 1) simply describes them as 'wise men' and they are traditionally considered to be philosophers or astrologers. The Gospel gives no number but because three different types of gifts are named, gold, frankincense and myrrh, three has been taken to be the number of wise men.
The names given to them, Caspar, Balthazar and Melchior, only date back to the 9th century. In paintings of the Adoration of the Kings (or Magi) one of them is usually represented as old, another in his prime and the third youthful; in some cases Balthazar is black.