The answer is: Abraham

Gen 17:5

When we think of "father of a great multitude," it really encapsulates not just Abraham’s legacy but also the expansive narrative of faith communities stemming from him. The name "Abraham," which signifies this great promise, showcases the incredible journey he undertook. He's a foundational figure in Judaism, Christianity, and Islam, illustrating how interconnected these faiths are through shared ancestors.

The story of Abraham isn't just about becoming a father to countless descendants—it's also about his courageous leaps of faith. For instance, imagine uprooting your family, leaving behind the familiar, and venturing into unknown territory just because you feel a divine nudge! That requires more than just great faith; it demands profound trust and a desire to embrace the unknown.

Let's not forget the fascinating theology encapsulated in God’s promise to Abraham. In Genesis 12, God tells him He will bless him, make his name great, and introduce a ‘great nation’ through him. Abraham's narrative echoes throughout scripture; take note of the many 'tests of faith' he faces. The covenant with Abraham illustrates the vital principle of relationship—between God and humanity, yes, but also amongst humanity itself. And oh, the fact that both Judaism and Christianity refer to Abraham as “the father of the faithful” highlights his importance across cultures and centuries!

The echoes of Abraham's faith permeate scripture, encouraging believers today to embrace their journey—crises, treasures, and all—living out the transformative power of faith just as he did.