 He remained a resident of the United States for most of his adult life, holding teaching positions at institutions such as the University of Minnesota and the State University of New York at Stony Brook.He was a friend and acolyte of Saul Bellow early in his career, although this relationship was damaged by Ludwig's extramarital affair with Bellow's then-wife Sondra; Ludwig was the basis of the character Valentine Gersbach in Bellow's novel "Herzog".Ludwig's novels include "Confusions" (1963), "Above Ground" (1968), and "A Woman of Her Age" (1973).