1493-1552. Swedish Reformer. Also “Olaus” or “Olaf.” Born at �rebro, he (like his brother Laurentius) was educated at Wittenberg and witnessed there the posting of the Ninety-Five Theses.* His 1529 manual was the first vernacular service-book of the Reformation. At the 1527 Diet of Västeras an order for preaching of the pure Word of God ended the Roman ascendancy. Petri prepared a Swedish Mass in 1531, and a collection of songs. His Postils also determined Swedish religious instruction. In 1540 he retired after a failure to report a murder plot against the king. Between 1526 and 1531 he produced sixteen Swedish books (there had before been only eight in the vernacular). He adapted Luther's work, and by his death had transformed the Swedish ecclesiastical scene.