  (Abridged) We aim at linking the dynamical and radiative properties of the
remnant of SN 1987A to the geometrical and physical characteristics of the
parent aspherical SN explosion and to the internal structure of its progenitor
star. We performed 3D hydrodynamic simulations which describe the long-term
evolution of SN 1987A from the onset of the SN to the full-fledged remnant at
the age of 50 years, accounting for the pre-SN structure of the progenitor
star. The simulations include all physical processes relevant for the complex
phases of SN evolution and for the interaction of the SNR with the highly
inhomogeneous ambient environment around SN 1987A. From the simulations, we
synthesize observables to be compared with observations. By comparing the model
results with observations, we constrained the initial SN anisotropy causing
Doppler shifts observed in emission lines of heavy elements from ejecta, and
leading to the remnant evolution observed in the X-ray band in the last 30
years. In particular, we found that the high mixing of ejecta unveiled by high
redshifts and broadenings of [FeII] and $^{44}$Ti lines require a highly
asymmetric SN explosion channeling a significant fraction of energy along an
axis almost lying in the plane of the central equatorial ring around SN 1987A,
roughly along the line-of-sight but with an offset of 40 deg, with the lobe
propagating away from the observer slightly more energetic than the other. We
found unambiguously that the observed distribution of ejecta and the dynamical
and radiative properties of the SNR can be best reproduced if the structure of
the progenitor star was that of a blue supergiant resulted from the merging of
two massive stars.
