According to Judges, the left-handed judge was Ehud.
Judges 3 describes Ehud as a Benjaminite chosen to deliver Israel from Eglon, king of Moab. He made a short, double-edged sword and strapped it to his right thigh, a position that allowed him to conceal it because weapons were commonly worn on the left side.
Ehud gained access to Eglon by presenting tribute and then requesting a private audience. The narrative says he used his hidden sword to kill the Moabite king before escaping and rallying the Israelites. Israel subsequently defeated the Moabites, and the land had peace for eighty years.
The detail that Ehud was left-handed is unusually specific in the biblical descriptions of judges. It is sometimes interpreted as a reference to a physical distinction or to a group of Benjaminites known for unusual handedness. Ehud is not the same figure as Othniel, Gideon, or Jephthah, who appear elsewhere in Judges.