For over half a century, starting around 1960, physics education was put under the intellectual microscope of a London-based university lecturer--Dr John Warren. His scrutiny of physics textbooks and examination papers in particular led him to conduct a sustained assault on error, ambiguity and lack of rigour in the presentation of our subject. This biographical article attempts to convey something of the nature of the man and his mission, and perhaps to sow the seeds of the reform for which he strove.