Who was Othniel?

Judges 1:13 (ESV)

13 And Othniel the son of Kenaz, Caleb’s younger brother, captured it. And he gave him Achsah his daughter for a wife.

He was Caleb’s nephew. Thus, in his taking of Caleb’s daughter Achsah in marriage, we see two generations of Israelites interacting—Caleb's and Othniel's.