I have always thought of him as Julian the Mediocre.
Sulpicius Severus in his Life of Martin of Tours describes a confrontation between Martin and the Caesar Julian at the place now called Worms. Martin demands his discharge from the army. "Up till now I have fought for you; allow me now to fight for God...I am a soldier of Christ; I am not allowed to fight."
Julian, called a "tyrant," is furious and accuses Martin of cowardice. Martin offers to stand unarmed in front of the front lines in the next day's battle. Martin was kept in prison overnight to ensure that he would do as promised. Instead, the next day the enemy sends envoys to sue for peace.