William of Santo Stefano

The dedication to Brother William (frere Guillaume in the text) in the Chantilly manuscript of the rhetoric and logic
The colophon identifying Brother William (frere Guillaume) in the Vatican manuscript of the order's documents

William of Santo Stefano, in Italian Guglielmo di Santo Stefano (fl. c. 1278–1303), was an Italian nobleman, historian and patron of letters. He was an active member of the Knights Hospitaller in Outremer, northern Italy and Cyprus, where he was commander from at least 1299 until 1303.

William was one of the most educated Hospitallers of the age. He commissioned translations from Latin into Old French of classical works of rhetoric and logic as well as legal and devotional documents from the Hospital's archives. He also wrote original legal and historical works in Old French.