The answer is: Hagar

Genesis 16:1-2 - Sarah, doubting that she could have children, suggested that Abraham have a child with her Egyptian servant, Hagar, leading to the birth of Ishmael.

Sarah's suggestion to Abraham to have a child with Hagar gives us a fascinating insight into ancient customs and family dynamics. It's a storyline filled with tension and cultural norms that, at first glance, might seem baffling to modern readers. In those days, it was not uncommon for a man to have a secondary wife or concubine to build his family, especially if the primary wife was struggling with infertility.

Hagar, an Egyptian, represents a world beyond the direct lineage of Abraham and Sarah. The birth of Ishmael is significant; it sparks the beginnings of the Arab lineage, making Ishmael a key figure in the stories of the Middle East. Interestingly, many Islamic traditions hold Ishmael in high regard, emphasizing his connections to both Jewish and Islamic heritage. In the grand narrative of biblical history, Hagar becomes a symbol of struggle and survival, as she communicates with God when she feels abandoned.

Additionally, this narrative touches on themes of faith and patience; Sarah’s doubts prompt decisive, albeit desperate, actions that set the stage for complexities in their family, echoed in later biblical tales of sibling rivalry—such as that of Isaac and Ishmael, or Jacob and Esau. Ultimately, Sarah's story invites reflection on the diverse ways humanity navigates its family and spiritual journeys, sharpening our understanding of sacrifice, competition, and faith.