Manga critic Jason Thompson declared Toriyama's art influential, saying that his "extremely personal and recognizable style" was a reason for "Dragon Ball"'s popularity. He points out that the popular "shōnen" manga of the late 1980s and early 1990s had "manly" heroes, such as "City Hunter" and "Fist of the North Star", whereas "Dragon Ball" starred the cartoonish and small Goku, thus starting a trend that Thompson says continues to this day. Toriyama himself said he went against the normal convention that the strongest characters should be the largest in terms of physical size, designing many of the series' most powerful characters with small statures. Thompson concluded his analysis by saying that only Akira Toriyama drew like this at the time and that "Dragon Ball" is "an action manga drawn by a gag manga artist." However, James S. Yadao, author of "The Rough Guide to Manga", points out that an art shift does occur in the series, as the characters gradually "lose the rounded, innocent look that established in "Dr. Slump" and gain sharper angles that leap off the page with their energy and intensity."