I discuss the early developments of string theory with respect to its connection with gauge theory and general relativity from my own perspective. The period covered is mainly from 1969 to 1974, during which I became involved in research on dual string models as a graduate student. My thinking towards the recognition of string theory as an extended quantum theory of gravity is described. Some retrospective remarks on my later works related to this subject are also given. 1. Prologue : an encounter with the dual string model I entered the graduate school of Hokkaido University, Sapporo, in April, 1969. My advisor, Akira Kanazawa who was an expert in dispersion-theoretic approach to strong interactions, proposed having a seminar on Regge pole theory regularly every week together with a few other students. Comparing with various marvelous theories which I had learnt during undergraduate studies, however, the Regge pole theory was somewhat disappointing for me. I felt that it was too formal and phenomenological in its nature without much physical content, except for interesting mathematical physics related to the notion of complex angular momentum. Looking for some more favorable topics, I became interested in studying the quantum field theory of composite particles, which, I thought, might be useful to explain the Regge-pole behavior from the dynamics of fundamental particles. I read many papers related to this problem such as those on compositeness criteria, on the definition of asymptotic field for a composite particle, and especially on the Bethe-Salpeter equation. Although I felt that this subject was not yet what I really would want to pursue, I learnt much about quantum field theory by studying these papers. Invited contribution to the book ”The Birth of String Theory”.