Eliezer ben Nathan (Hebrew: אליעזר בן נתן) of Mainz, Ra'aven (ראב"ן), was a halakist and liturgical poet. As an early Rishon, he was a contemporary of the Rashbam and Rabbeinu Tam, and one of the earliest of the Tosafists.

He was the son-in-law of Rabbi Eliakim b. Joseph of Mainz, a fellow student of Rashi. Through his four daughters Eliezer became the ancestor of several learned families which exerted a great influence upon religious life in the subsequent centuries.

One of his great-grandsons was R. Asher b. Jehiel (ROSH), father of R. Jacob, author of the Ṭurim.