Dennis first appeared in Beano No. 452 (March 17th, 1951). He didn't wear his stripey jersey, though - that would come a few weeks later - and he hadn't bumped into his future best pal Gnasher yet.
The artist was David Law, and he would draw Dennis the Menace comics until 1970. He also drew Corporal Clott for The Dandy and Beryl the Peril for The Topper.