Liquid crystals are usually not thought of as ‘simple’ liquids. Nevertheless, a surprising number of features of liquid crystals can be reproduced in computer simulations of very simple model systems, viz. hard ellipsoids of revolution and parallel spherocylinders. In particular, depending on the density and the shape of the hard-core particles, stable isotropic, nematic, smectic and crystalline phases are found. The existence of hard-core models for liquid crystals is important for two reasons. First of all, they can be used to test molecular theories for the static and dynamic properties of liquid crystals. And secondly, they may provide a starting point for thermodynamic perturbation theories. These hard-core models exhibit large pre-transitional fluctuations in the vicinity of some of the phase transitions, similar to those observed in real mesogens. Examples are given of the ‘experimental’ consequences of nematic and smectic precursor effects.