Lê Văn Duyệt
Gia Long's death coincided with the re-establishment of the Paris Missionary Society's operations in Vietnam, which had closed in 1792 during the chaos of the power struggle between Gia Long and the Tây Sơn brothers before Vietnam was unified. In the early years of Minh Mạng's government, the most serious challenge came from one of his father's most trusted lieutenants and a national hero in Vietnam, Lê Văn Duyệt, who had led the Nguyễn forces to victory at Qui Nhơn in 1801 against the Tây Sơn dynasty and was made regent in the south by Gia Long with full freedom to rule and deal with foreign powers.