High entropy alloys (HEAs) belong to a new class of materials with multiple principal components that are chemically concentrated in less explored phase spaces. Since the initial discovery, HEAs have attracted tremendous interest for their remarkable structural diversity and associated properties, including high strength and high ductility. Underlining the structural diversity is the metastability of HEAs, to which a key contributor is the lattice distortion effect that emerges as a direct consequence of interplay between atomic size misfits and chemical disorder. Lattice distortion also directly contributes to alloy strengthening and ductility. Despite the recognized significance, however, the critical knowledge of lattice distortion is still missing in the study of HEAs. Here, we first report on the nature of lattice and chemical disorder in a single-phase HEA and determine its local atomic structure. Our results uncover the manifestation of disorder at three different length scales, namely, the lattice distortion at the atomic scale, the chemical disorder at the nm scale, and the emergence of nanoscopic shear at the mesoscopic scale. The multiscale disorder leads to hierarchical strengthening, unlike anything that we know before about metals. This finding provides the structural basis for theoretical understanding of structure-property relationships in HEAs, and demonstrates the randomness of disorder as a new dimension for designing future strong and ductile alloys.