His biological mother is Bilhah, but he is regarded as the son of Rachel who provided Bilhah her maidservant as a concubine for Jacob in response to her barenness. This is in contrast to her sister Leah who has already born four sons for Jacob. Rachel is overjoyed at the birth, saying "I have had a great struggle with my sister, and I have won" (Genesis 30:8, NIV).
Rachel then names him. Naphtali means my struggle.