In this talk I will discuss how string theorists used the notion of the ‘real world’ (in a broad sense) while developing their theory. With this, I aim to bring to the fore an evolution of what was considered ‘realistic’ in particle theory, from the early 1970s, when theoretical particle physics was still very much concerned with experimental data, into the highly mathematical string theory program of the mid-1980s. The framework of my talk is as follows: first, I will sketch how, shortly after the formulation of the ‘Standard Model’ in the early 1970s, particle theorists started searching for a more fundamental theory underlying it—in particular I will single out grand unified theories and supergravity. Secondly, I will describe the development of superstring theory by John Schwarz and Michael Green in the early 1980s, and point out how they related their theory to ‘known physics’. Then, I will discuss string theory’s breakthrough in 1984/1985, and point out how a dramatically broadened up notion of being potentially ‘phenomenologically realistic’ was central here. Finally, I will sketch how in the late 1980s, string theorists developed their theory into multiple directions to potentially connect it to different notions of the ‘real world’. The talk is based upon a chapter-in-progress of my PhD thesis.