Colonel Mathieu was a high-ranking Belgian military officer in East Africa, under the command of General Tombeur. His command included Major Boucher, and Lieutenants Henri Defense (Indiana Jones) and Remy Baudouin.
In December 1916, after a battle led by Boucher in which Jones turned a retreat into victory by capturing a machine gun and rallying the Force Publique, Mathieu commended both Boucher and Jones for the victory, and passed along the congratulations from General Tombeur, including a promotion for Jones to captain.
Mathieu then gave Boucher and Jones a mission: to cross the Congo basin to pick up a shipment of machine guns and mortars at Cape Lopez, for use in the assault on Tabora. He felt that the pairing would provide Jones with a seasoned military mentor, and Boucher with energy and quick thinking, but privately expressed his confidence in Jones completing the mission.