Simple answer: Avraham Aveinu
Addressing what the original question really is asking: Modern kiruv (i.e. modern Baalei Tseuvah) only started when you started having “modern” OTD (i.e. Jews leaving the Orthodox community without converting to Islam or Christianity). That was very rare until the 19th century (note that in the past, it wasn’t so much that being a Yid was illegal, but that not being part of the official government religion was considered illegal). The big “boom” in the Kiruv movement began after World War II, and was accelerated as the Jewish “boomers” came to an age where they could ignore their almost universally secular parents and start reasserting their Jewishness.