The term McKenzie friend stems from McKenzie v McKenzie  P 33;  3 WLR 472 (CA). As recorded in the judgment of Davies LJ:
Mr Hanger is alive today! He became Ian Hanger AM QC and a keen amateur photographer. He delivered an excellent lecture in which he recounted his experience of appearing in front of Lloyd-Jones J as a freshly admitted Australian barrister (he literally rode to work each morning on the Clapham omnibus!). The lecture is below and keyed to start at the description of the case. It skips the part where he recounts the captain of his ship to the United Kingdom shooting himself in the head.