Zeruiah was David’s sister (see 1 Chronicles 2:16). She gave birth to three sons, Joab, Abishai, and Asahel. These sons were fiercely loyal to David, but they still caused great problems for him since they trusted in human strength as opposed to leaving vengeance to God.1
18 And the three sons of Zeruiah were there, Joab, Abishai, and Asahel. Now Asahel was as swift of foot as a wild gazelle.