Mansa Musa came to power as the king of the West African empire of Mali in 1312. While Europe was dealing with famine and civil wars, African kingdoms were flourishing.
Mansa Musa expanded the empire of Mali and took control of important trade routes between the Mediterranean and the West African coast. The territory of Mali was also rich in natural resources like gold. Combine the control of trade routes, with a ton of natural resources, and you get a very rich kingdom.
Besides being the richest person on earth, Mansa Musa was also a devout Muslim, so in 1324 he decided to make the pilgrimage to Mecca.
And he did that pilgrimage in style. He brought with him a ton of people, some say tens of thousands of soldiers, civilians, and slaves. He also brought one hundred camel loads of gold, which is a very large sum.
He stopped in cities along the way, including some in Egypt. He spent freely, gave money to the poor, bought souveniers, and had houses and mosques built along the way.
He managed to give away so much gold that he may have single handedly destabilized the economy of Egypt by causing mass inflation that they took years to recover from.
As he travelled to Mecca, the news of this rich Afican king spread throughout the world, and Mali was included in the 1375 Catlan Atlas, which was one of the most important mediaeval world maps. And this is where the famous image of him comes from.
After his pilgrimage, he built a mosque and university in Timbuktu, giving the city a stronger reputation, and attracting intellectuals from all over the Islamic world.