After his achievement of fame with The Songs of a Sentimental Bloke (1915), C. J. Dennis took considerable care with the management of his public image and remained reticent about much of his early life, including his time at the Gadfly. Dennis's role in this lively, satirical and radical weekly, which first appeared early in 1906 in Adelaide, has received little attention from his biographer, Alec Chisholm. He co-founded the paper with Archie (A. E.) Martin and Beaumont Smith, edited it for the first half of its life, and was a prolific contributor; and this period is revealing about his character, his development as a writer, and his private and public concerns. Among other things, the absence of information about Dennis's Gadfly days has contributed to the downplaying of the radical political views he held until he was at least forty. This article attempts to piece together a picture of his involvement in a significant, if little-known, piece of Australian newspaper history.