Sebastian Krelj, also known as Sebastjan Krelj, Sebastijan Krelj or Boštjan Krelj (1538 – 25 December 1567) was a SloveneProtestant reformer, writer, pastor, linguist and preacher and regarded as one of the most educated Slovene Protestants of the 16th century.
Krelj had a wide linguistic and philologic knowledge: besides Slovene, German and Latin, he knew Ancient Greek, Hebrew, Croatian and Glagolitic literature. Krelj put the central dialect into context of dialects spoken by Istrians, the inhabitants of the Vipava Valley and Lower Carniolans. He introduced some changes to the Latin script originally adopted by Trubar from the German. He consistently differentiated the phonemes /s/ /z/ /t͡s/ /ʃ/ /ʒ/ /t͡ʃ/ /t͡ɕ/ /ə/ (written by Krelj as ſ s z ſh sh zh ch à/è, modern orthography s z c š ž č ć e). His reforms were taken up by Jurij Dalmatin in the first translation of the entire Bible to the Slovene. In 1583, they were codified by Adam Bohorič in his grammar book Arcticae horulae succisivae.