Converts have been involved with seforim in many capacities. But, there is one book which was actually authored by a convert – Zera Yitzhak, Amsterdam 1789. This book is on Pirkei Avot and was written by R. Yitzhak (b. Avraham) Graanboom. R. Yitzhak was born in Sweden a non-Jew. His father Jacob moved his family to Amsterdam in 1749. At age 69, after moving to Amsterdam, Jacob and his wife Leah converted to Judaism. At the time, Jacob took the name Avraham. His youngest son Mattis, also converted and became Yitzhak (his full name appears to be Aharon Moshe Yitzhak, however, in his book both on the title page and the approbation he is referred to only as Yitzhak, perhaps these names were added later, or he didn’t use them).

R. Yitzhak was extremely successful in his studies and was widely respected within the Amsterdam community; so much so, that when he attempted to move to Israel, R. Saul (ben Aryeh Löb) Löwenstamm (1717-1790) – then Chief Rabbi of Amsterdam – convinced him not to for the sake of the Amsterdam community. R. Yitzhak was for a short period of time a gem cutter, after which he moved to full time study and working. After R. Löwenstamm died, R. Yitzhak became the interim chief Rabbi of Amsterdam. Later, he became the Chief Rabbi of a new synagogue in Amsterdam, Adat Yeshurun. As this was a new synagogue, there were some from his old synagogue who were upset with the move. R. Yitzhak was known as “Yitzhak the Ger” (Yitzhak the Convert), some members of the old synagogue began referring to him instead as “Yitzhak Getz” (Yitzhak the Fool).

R. Yitzhak died in 1807 and his epitaph reads as follows:

זאת מצבת קבורת אדונינו מורנו ורבינו אב”ד ור”מ דקהלתנו, הנודע שמו בישראל בשם הגאון הצדיק החסיד מוהר”ר אהרן משה יצחק בן כ”ה אברהם זצוק”ל. רועה צאן עדת ישרון, גאה וגאון השליך נגדו, הצנע היה לכתו, רק לאמונה גבר בארץ, להורות עם ה’ את הדרך ישכון אור, להטות לבבם ליראת ה’ כל הימים, ולגלות למסור אזנם, ויקם עדות ביעקב ותורה שם בישראל, אף אם הציון הלז יכסה את גויתו, אהבתו תשאר תקועה
בלבנו, כי בזרע יצחק עוד יאיר שמשו ואור חכמתו ותורתו לעד בעולם

This is the monument of our master, our teacher, our Rabbi, the Chief Rabbi and Teacher of our community, who is known as the great one, pious, and righteous Rabbi Aharon Moshe Yitzhak son of the wise on Avraham ztsuk”l. The leader of Congregation Adat Yeshurun, the great and high one, who was humble in his ways, his relied upon faith, and taught the path to light, to lead their hearts to fear God all their days, and to reveal the ethical path to their ears, and he upheld the congregation and gave Torah to Israel, even though this monument covers his body, our love for him remains in our hearts, with the seed of Yitzhak will still guide by his light, and his light of wisdom and Torah will remain forever.

After he died, there were some who questioned some of his minor innovations and his son, Yisrael printed Melitz Yosher, to defend these practices.