Othniel was the first judge of Israel mentioned in the Book of Judges.
Judges 3 presents Othniel son of Kenaz as Israel's first judge after the death of Joshua. The Israelites had fallen under the rule of Chushan-Rishathaim, king of Aram-Naharaim, and were oppressed for eight years. When they cried out, the biblical narrative says God raised up Othniel as a deliverer.
Othniel defeated the foreign ruler, and the land then had peace for 40 years. He is the first judge in the book's recurring pattern: Israel turns away, suffers oppression, calls for help, and is rescued by a leader empowered by God.
Othniel is also mentioned in Joshua, where he captures Debir and receives Achsah, Caleb's daughter, in marriage. Deborah, Gideon, and Samson were later judges, not the first. Othniel's position is about the sequence of judges in the biblical narrative, not necessarily a modern historical ranking independently confirmed by archaeology.