The original idea is perhaps to be credited to the German exegete, Gerd Theissen (in Sociology of Early Palestinian Christianity [Philadelphia: Fortress, 1978], pp. 14-15; earlier: “Wanderradikalismus: Literarsoziologische Aspekte der Überlieferung von Worten Jesus im Urchristentum,” Zeitschrift für Theologie und Kirche 70 (1973), pp. 255-256). It has also been pursued vigorously by Gerald Downing (in Christ and the Cynics [Sheffield: JSOT Press, 1988], among other titles) in the U.K. But in American circles it is Burton Mack (A Myth of Innocence [Philadelphia: Fortress, 1988], pp. 53-77) who has made the claim stick, amid great controversy.