You know how “smart” in comics actually means stupid? This time, as they often did in Suicide Squad, John Ostrander and Kim Yale pulled a reversal: a character introduced as a superficial fanatic, never billed as or discussed otherwise, who was smart as a whip. Wikipedia tells me he only appeared in twenty-two comics issues, ever, associated only with this series, but they were solid gold.
Victor von Doom debuted in Fantastic Four #5, in July 1962, and his origin and general depth of character were presented in January 1964, in the FF Annual #2. This identified him as the ruler of Latveria almost immediately in the history of the character, unlike the political history of Magneto for instance, who first appeared in September 1963 and was retconned into being a survivor of the Holocaust in 1981.