A gentile heard about the honor paid to the High Priest in Jerusalem and decided he wanted the office for himself. He came first to Shammai and asked to convert on the condition that he be made High Priest. Shammai refused outright. The demand was ridiculous, he said, and drove the man out with a builder's rod.
The man then came to Hillel. Hillel, famously patient, welcomed him warmly and accepted him as a student, with one condition: that he first learn everything a Jew is required to know. The convert agreed and began his studies.
Months later, reading through the Torah, he came across the verse that stopped him: "The stranger who approaches the sanctuary shall die" (Numbers 1:51). Confused, he went to Hillel and asked who this rule applied to. Hillel answered, "It applies to every Israelite who is not a priest, even King David himself. David was of the tribe of Judah, and even he could not approach the altar of the Lord."
The man laughed at his old ambition. If David could not approach, he thought, how could a convert demand the priesthood on day one? He accepted his place and converted in earnest.
He had two sons. One he named Hillel, after the master who had received him. The other he named Gamliel. They were known ever after as the proselytes of Hillel, and their father was Onkelos, the convert who eventually translated the entire Torah into Aramaic. That translation, the Targum Onkelos, became the standard Aramaic version of the Torah for the whole Jewish world (Gaster, Exempla No. 31).
The man who came looking for the crown of the High Priest walked out with something more enduring: every Torah scroll in the diaspora is read through the lens his translation provided.