Musa I of Mali was the richest man to have ever existed with $400 billion (according to 2010 dollar value)
Musa I of Mali was the richest man to have ever existed with $400 billion (according to 2010 dollar value) wealth and was so generous with gold that the metal was devalued for a whole decade.
Musa Kieta I of Mali was the tenth Mansa (king), and conqueror and emperor of the West African Mali Empire during early 14th century. He is said to have conquered over 24 cities along with their surrounding districts, villages, and estates. During his reign, he made a fortune by exploiting salt and gold production in Mali which also made him immensely wealthy. Being a devout Muslim, he made a pilgrimage to Mecca between 1324 and 1325 with 60,000 men and 12,000 slaves who carried 4-pounds of gold bars each.
On his way, Musa was so generous with his gold that the economy collapsed in the regions he passed through, and the cities of Cairo, Medina, and Mecca had to face a decade during which gold had little value. In order to help the gold market, Musa borrowed as much gold as he could carry at high-interest rates from money-lenders in Cairo.(source)