Final answer:
Mansa Musa was the richest person ever because he controlled the Mali Empire, enriched by the trans-Saharan trade, and demonstrated his wealth through his lavish spending during his pilgrimage to Mecca, which impacted economies like Cairo's for years.
Step-by-step explanation:
Mansa Musa is known as the richest person ever primarily because he controlled a vast empire that included crucial trade routes for gold and salt. During his reign from 1307-1337, he expanded the Mali Empire to its greatest size, which significantly increased his wealth due to tributes paid in gold and other valuable commodities. Mansa Musa's wealth was so immense that during his pilgrimage to Mecca in 1324-25, he famously distributed gold so lavishly that it caused inflation in Cairo for twelve years. This story of his generosity was documented by chroniclers like al-Umari and noted in various historical sources. Furthermore, Mansa Musa invested in his empire's infrastructure and culture, rebuilding the city of Timbuktu into a center of learning and showcasing his wealth and power through the creation of architectural artifacts and monuments.