Why was Suleiman called both "the Magnificent" and "the Lawgiver"?

Suleiman I ruled the Ottoman Empire from 1520 to 1566, and he is remembered under two nicknames that say different things. In the West he was "the Magnificent". To his own subjects he was always Kanuni Suleiman, "the Lawgiver".

"Magnificent" fits the conqueror and the showman. He took Belgrade in 1521 and Rhodes in 1522 and broke the strength of the Kingdom of Hungary at Mohács in 1526. In 1532, competing with the Habsburgs, he wanted to show his superiority in every field and had Venetian merchants make him a four-tiered crown for 115,000 ducats. His reign is seen as the high point of Ottoman political and cultural life.

"Lawgiver" points at something quieter. The Sharia, the sacred law of Islam, was outside the sultan's power to change. But a second body of law, the kanuns, covering criminal law, land tenure and taxation, depended on the sultan's will. Suleiman collected the judgments of the nine sultans before him, removed duplications, chose between contradictory rulings and issued a single code, working with his chief judge Ebussuud Efendi. The result lasted more than three hundred years.

Now the twist. It is unclear when "the Lawgiver" first became his nickname. It is entirely absent from sixteenth- and seventeenth-century Ottoman sources and may date from the early eighteenth century. The age's achievements were also the work of many people, from viziers to the chancellor Celalzade Mustafa, who helped build Suleiman's image as an ideal ruler.