Trương Định sometimes known as Trương Công Định, was a mandarin

Mandarin (bureaucrat)

A mandarin was a bureaucrat in imperial China, and also in the monarchist days of Vietnam where the system of Imperial examinations and scholar-bureaucrats was adopted under Chinese influence.-History and use of the term:...

 in the Nguyễn Dynasty of Vietnam

Vietnam

Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

 under Emperor Tự Đức. He is best known for leading a guerrilla army in southern Vietnam against the French invasion

Colonization of Cochinchina

The French conquest of Cochinchina – which was the European name for the southern part of Vietnam – occurred in two phases between 1858 and 1867.-Historical background:...

 in defiance of the emperor. He refused to recognise the 1862 Treaty of Saigon

Treaty of Saigon

The Treaty of Saigon was signed on June 5, 1862, between representatives of the French Empire and the last precolonial emperor of the Nguyễn Dynasty, Emperor Tự Đức. Based on the terms of the accord, Tự Đức ceded Saigon, the island of Poulo Condor and three southern provinces of what was to become...

 that ceded Vietnamese territory to France.

The son of a military mandarin from central Vietnam, Định moved south when his father was posted to Gia Định as the provincial commander.