 It began with the Euler beta function model of Gabriele Veneziano in 1968 for a 4-particle amplitude which has the property that it is explicitly s–t crossing symmetric, exhibits duality between the description in terms of Regge poles or of resonances, and provides a closed-form solution to non-linear finite-energy sum rules relating s- and t- channels.The Veneziano formula was quickly generalized to an equally consistent "N"-particle amplitude for which Yoichiro Nambu, Holger Bech Nielsen, and Leonard Susskind provided a physical interpretation in terms of an infinite number of simple harmonic oscillators describing the motion of an extended one-dimensional string, hence came the name "string theory.