Ahmad al-Mansur (Arabic: أبو العباس أحمد المنصور بالله, romanized: Abū l-ʿAbbās Aḥmad al-Manṣūr biʾllāh; 1549 – 25 August 1603), also known as al-Dhahabī (Arabic: الذهبي, lit. 'the Golden') was the Saadi Sultan of Morocco from 1578 to his death in 1603, the sixth and most famous of all rulers of the Saadis. Ahmad al-Mansur was an important figure in both Europe and Africa in the sixteenth century. His powerful army and strategic location made him an important power player in the late Renaissance period. He has been described as "a man of profound Islamic learning, a lover of books, calligraphy and mathematics, as well as a connoisseur of mystical texts and a lover of scholarly discussions."

Ahmad was the fifth son of Mohammed ash-Sheikh, who was the first Saadi sultan of Morocco. His mother was Lalla Masuda. After the murder of Mohammed in 1557 and the following struggle for power, two of his sons, Ahmad al-Mansur and Abd al-Malik, had to flee their elder brother Abdallah al-Ghalib (1557–1574), leave Morocco and stay abroad until 1576. The two brothers spent 17 years among the Ottomans between the Regency of Algiers and Constantinople, and benefited from Ottoman training and contacts with Ottoman culture. More generally, Ahmad al-Mansur "received an extensive education in Islamic religious and secular sciences, including theology, law, poetry, grammar, lexicography, exegesis, geometry, arithmetics, algebra, and astronomy."

In 1578, Ahmad's brother, Sultan Abu Marwan Abd al-Malik I, died in battle against the Portuguese army at Ksar-el-Kebir. Ahmad was named his brother's successor and began his reign amid newly won prestige and wealth from the ransom of Portuguese captives.

Al-Mansur began his reign by leveraging his dominant position with the vanquished Portuguese during prisoner ransom talks, thus collecting enough money to fill the Moroccan royal coffers. Shortly after, he commissioned the great architectural symbol of this new birth of Moroccan power, the El Badi Palace in Marrakesh, a huge and lavish riad-style palace which he used to receive ambassadors and to host celebrations. Construction began in December 1578 and was only finished in 1593 or 1594.

Eventually, the coffers began to run dry due to the great expense of supporting the military, extensive spy services, the palace and other urban building projects, a royal lifestyle and a propaganda campaign aimed at building support for his controversial claim to the Caliphate.

Morocco's standing with the Christian states was still in flux. The Spaniards and the Portuguese were seen as infidels, but al-Mansur knew that the only way his sultanate would thrive was to continue to benefit from alliances with other Christian economies. To do that, Morocco had to control sizeable gold resources of its own. Accordingly, al-Mansur was drawn irresistibly to the trans-Saharan gold trade of the Songhai in hopes of solving Morocco's economic deficit with Europe.

Al-Mansur developed friendly relations with England in view of an Anglo-Moroccan alliance. In 1600, he sent his Secretary Abd el-Ouahed ben Messaoud as ambassador to the Court of Queen Elizabeth I of England to negotiate an alliance against Spain.

Al-Mansur also wrote about reconquering al-Andalus for Islam from the Christian Spanish. In a letter dated 1 May 1601, he wrote that he also had ambitions to colonize the New World. He envisioned that Islam would prevail in the Americas and that the Mahdi would be proclaimed from the two sides of the oceans.