Born January 25, 1907 in Lamar, Colorado, Gregg attended Racine High School in Wisconsin until 1925, when he won second prize in a poster designing contest and was advised to go to art school. He graduated from the Layton School of Art in Milwaukee in 1928, but found it difficult to get work at that time. He began accepting freelance assignments, including several from the Western Printing & Lithographing Company in Racine. In 1935, when one of Western’s staff artists took a temporary leave of absence, Gregg was hired as his replacement. Russell Stone, Western’s art director, liked Gregg’s work and offered him a regular position.
In 1943, new art director Bill Strohmer and his assistant, George Frederiksen assigned Gregg to do covers for Dell paperbacks. Strohmer or Frederiksen would generally provide colour sketches which Gregg either fleshed out or adapted. He often used Western’s secretaries and stenographers as models for the beautiful women on his covers. Of the 176 covers he produced for Western Gregg’s own favourites include Dell 115 (The Broken Vase) and Dell 229 (Candidate for Love).
Also during his tenure at Western, Gregg drew Disney and Warner Brothers comic strips and all back covers for the Little Golden Books series.
He worked with an airbrush, and it was his extraordinary technique with that apparatus which made the Dell covers of the 1940s unique. He describes his own style as a combination of graphic design and stylized realism. In addition to his airbrush work, he also produced covers in oils and watercolours, with pen-and-ink and with photography.