Clue: Theologian, until converted by article, right behind revolutionary force (6,6)
Answer: MARTIN LUTHER
Explanation: Definition: Theologian
A charade of MAR, a reversal ('revolutionary') of RAM ('force') plus TINLU, an anagram ('converted') of 'until' plus THE (definite 'article') plus R ('right'), with 'behind' indicating the order of the particles.