The Onderonian resistance was an underground resistance movement against the Mandalorian Neo-Crusaders formed by Vaklu during the Mandalorian Wars.
Vaklu, leader of the resistance.
When the Mandalorians had gained control over Onderon, a resistance was formed to end the control of Mandalorians on Onderon, the resistance had little effect until the Jedi entered the war and defeated the Mandalorians, liberating Onderon from Mandalorian control. Vaklu, commander-in-chief of the Onderonian military, led the resistance. Despite the minority of the resistance, the act of Vaklu leading the resistance made him a war hero, making many Onderonians support him.
During the Jedi Civil War the Jedi Exile went to Onderon and saw a civilian who claimed to be in the Onderonian resistance, but was falsely charged of being a Republic spy by Vaklu officers. The Jedi Exile vindicated him, however.
It was possible for the Jedi Exile to not get involved and let the civilian be taken away by Vaklu officers.