Musa I (c. 1280 – c. 1337), was the tenth Mansa ( “conqueror”or “emperor”) of the Islamic West African state known as the Mali Empire.
The Mansa Musa net worth was estimated to be approximately $400 billion USD inflation adjusted. Making him the historically richest person to ever live. This is over double the current net worth of the richest man in the world Jeff Bezos at $196.2 billion. The source of his massive personal wealth was his territories vast natural resources, which the most important was gold.
The Mali Empire consisted at the time of his reign of territory that is now part of Guinea, Senegal, Mauritania, Gambia, the former Ghana Empire, and modern Mali.
Musa conquered 24 cities and their districts. During his reign, Mali may have been the largest producer of gold in the world. While there is no way to accurately quantify his exact wealth, it is agreed upon by most scholars to be staggering and much more than even the richest people in the modern world. 
He became famous in 1324 when he made a pilgrimage to Mecca. During this journey, he caused mass inflation in Cairo by spending so much gold on the poor. Word of his wealth spread across the Mediterranean. He is included on the 1375 Catalan Atlas. He built the legendary Djinguereber Mosque in Timbuktu, which still stands today.