First appearance = Nickel Comics #1 (May 17, 1940) from Fawcett Comics:

"Warlock the Wizard" had a feature in the first seven issues of Fawcett's Nickel Comics, but it doesn't look like he even made it to the final issue (#8) of that book.

First (and only?) appearance in a new story from DC Comics = a cameo in Scooby-Doo! Team-Up in 2016 (issue #37 of the digital-1st version / #19 of the printed version):