American Weekly, in a 1952 article on calendar girls, called him "The Dean of Calendar Artists," and he's considered one of the Fathers of American "Good Girl" art. His first Brown and Bigelow work was, Dream Girl (1919), a copy of his American Weekly cover (see below). His pastels graced advertising, magazine covers, sheet music, and of course, calendars, for over 40 years. An athletic man (he taught boxing and baseball, in addition to art), his earliest art was not pretty girls, but men of action (military, sports, old west). Like Howard Chandler Christy who started depicting heroic men, he switched to the American girl with incredible and long-lived success. His healthy, girl-next door beauties appeared on Judge, Photoplay, College Humor, Life, Every Week, Shrine, Pictorial Review, Woman's Home Companion. Also in demand for ad art (Pepsi, Pompeian Skin Care, Oneida Silverware, Palmolive, Kissproof makeup).

A monograph on Armstrong, "Pin-Up Dreams: The Glamour Art of Rolf Armstrong" by Janet Dobson, Michael Wooldridge was published in 2001.