Jehovah was popularized by a catholic monk who lived in the 12th century AD. In fact "Jehovah" was never used before this! The form "Jehovah" results from reading the consonants of the Tetragrammaton with the vowels of the surrogate word Adonai. The dissemination of this form is usually traced to Petrus Galatinus, confessor to Pope Leo X, who in 1518 a.d. transliterated the four Hebrew letters with the Latin letters jhvh together with the vowels of Adonai, producing the artificial form "Jehovah." (While the hybrid form Jehovah has met much resistance, and is universally regarded as an ungrammatical aberration, it nonetheless passed from Latin into English and other European languages (Anchor Bible Dictionary, YAHWEH)
