Teólogo, con amplios conocimientos en matemáticas y astrología, fue uno de los literatos más cultos de su época y dominó el hebreo, el castellano y el latín.Tuvo como discípulos a Walcher de Malvern y Adelardo de Bath. Se convirtió al catolicismo a la edad de cuarenta y cuatro años, cambiando su nombre de Mosé Sefardí por el de Pedro Alfonso; su padrino fue el rey Alfonso I el Batallador. Su obra <i>Disciplina clericalis</i> fue muy difundida. La componen una gran cantidad de cuentos, en forma de apólogos, recogidos de proverbios árabes y orientales. Se hicieron traducciones del libro a diversas lenguas y sus asuntos, así como los modelos didácticos que proponía en ellos, influyeron en autores como Don Juan Manuel, Boccaccio, Chaucer o el propio Cervantes, entre muchos otros. Vicente de Beauvais realizó un compendio que incluyó en su <i>Speculum historiale.</i> Jacobo de la Vorágine también utilizó textos sobre el Islam de Pedro Alfonso para su <i>Leyenda dorada</i>. En <i>Dialogi contra iudaeos (Diálogo contra los judíos),</i> obra en la que desvela datos sobre su vida personal, como su conversión al catolicismo, utiliza los conocimientos que posee de la Biblia hebrea y de la literatura judía, y es el primero que utiliza la literatura tradicional hebrea y a sus exégetas para atacarlos con sus propios argumentos. Hacia 1116 tradujo y adaptó al calendario juliano el <i>Zij al-sindhind,</i> escrito hacia el 830 por al-Khwarizmi y reelaborado hacia el 1000 en Córdoba. Citaremos también <i>Epístola ad peripatéticos franciae</i> y <i>De dracone.</i> Su obra apologética fue utilizada por teólogos, polemistas e, incluso, por los predicadores de las Cruzadas.
Resumen biográfico extraído de Wikipedia en español: <blockquote>"Moshé Sefardí, posteriormente Petrus Alfonsi o Pedro Alfonso en homenaje a su protector, Alfonso I de Aragón, (Huesca, ¿1062? - ¿1140?), fue un escritor, teólogo y astrónomo español de origen judío y convertido al cristianismo en 1106."</blockquote>
Abstract from English Wikipedia: <blockquote>"Petrus Alphonsi was a Jewish Spanish physician, writer, astronomer, and polemicist, who converted to Christianity in 1106. He is also known just as Alphonsi, and as Peter Alfonsi or Peter Alphonso and was born Moses Sephardi). Born in Islamic Spain, he mostly lived in England and France after his conversion. He was born at an unknown date and place in the 11th century in Spain, and educated in al-Andalus, or Islamic Spain, largely the same as modern Andalucia. As he describes himself, he was baptized at Huesca, capital of the Kingdom of Aragon, on St. Peter's Day, 29 June 1106, when he was probably approaching middle age; this is the first clear date we have in his biography. In honor of the saint Peter, and of his royal patron and godfather, the Aragonese King Alfonso I he took the name of Petrus Alfonsi (Alfonso's Peter). By 1116 at the latest he had emigrated to England, where he seems to have remained some years, before moving to northern France. The date of his death is as unclear as that of his birth. He was famous as a writer during his lifetime, and remained so for the rest of the Middle Ages, with over 160 surviving medieval manuscripts containing works of his. The most common are his Dialogi contra Iudaeos (Dialogue Against the Jews), an imaginary conversation between a Jew and a Christian, and Disciplina Clericalis (A Training-school for the Clergy), in fact a collection of Eastern fables. Petrus was born a Jew while living in al-Andalus, and after he rose to prominence, he converted to Christianity. This environment gave him an advantageous knowledge of Christianity, Judaism and Islam that would later prove useful in his polemics. John Tolan mentioned in his book Petrus Alfonsi and His Medieval Readers that "Alfonsi's texts were received enthusiastically-he became an auctor, an authority to be quoted. His success was due in large part to his ability to bridge several cultures: a Jew from the [Muslim] world of al-Andalus." His knowledge of these different religions is what makes Alfonsi unique and why he is essential to be studied when looking at anti-Judaic polemics. Petrus' upbringing placed him in an atmosphere that provided a significant impetus to launch him as one of the most important figures in anti-Judaic polemics. According to Tolan, Petrus Alfonsi was reared in a society in turmoil: a place of chaos and political instability, where Judaism was in conflict with science, and Islam and Christianity were becoming a larger influence. His background was conveniently placed in the center of contention between religions and circumstances that surrounded his upbringing, and provided the framework for polemics that would shape Medieval Judaic perception."</blockquote>