NGC 7293, the Helix nebula, represents one of the rare instances in which theoretical predictions of stellar evolution can be accurately tested against observations since the precise parallax distance and the velocity and proper motion of the star are well known. We present numerical simulations of the formation of the Helix PN that are fully constrained by the (inferred) progenitor stellar mass, stellar evolution history, and star-interstellar medium (ISM) interaction. We have followed the evolution of the star from the early Asymptotic Giant Branch (AGB) phase to the PN stage and modeled the density and kinematical evolution of the expanding shells considering the observed relative motion of the star. In the simulations, multiple bow-shock structures are formed by fragmentation of the shock front where the direct interaction of the stellar wind with the ISM takes place.