Ο Gustavus III (Gustaf III, 1746-1792) was King of Sweden from 1771 to 1792. He was the son of Adolf Frederick and Louisa Ulrike of Prussia. In 1766 he married Sophia Magdalene of Denmark, with whom he had two sons.

During his reign, Gustavus III promoted culture and the arts, founding the Swedish Academy and supporting theatre and literature. In 1772, he staged a coup that strengthened royal power, limiting the power of the aristocracy and parliament. However, his authoritarian rule provoked opposition, leading to conspiracies against him.

Gustavus III became a Freemason in 1780 and introduced the ritual of the Strict System to Sweden. In the same year, he appointed his brother, the Duke of Södermanland (later Charles III), to the office of Grand Master of the Grand Lodge of Sweden. The Lodge bestowed upon him the title “Vicarius Salomonis” (Representative of Solomon).

Gustavus III’s contribution to the strengthening of Freemasonry in Sweden was significant, as he promoted Masonic values and supported the development of the order in the country. King Gustavus III was a prominent figure in Swedish Freemasonry, actively participating in and influencing the Masonic traditions of his time.

In 1792, during a masquerade ball, he was murdered by James John Ankarstrom, a member of an aristocratic conspiracy.