Some models will be rotated and arranged in the Blender world for artistic purposes.
The models have, however, all their transformations set to a (0,0,0) location, zero scale and zero rotations.
To restore the model to its zeroed position, simply select it and type in the keyboard:
Cntr+R – Clears all rotations
Cntrl+G – Restores location to (0,0,0)
Cntrl+S – Restores scale to original size
Examples of rotated models that can be reset to a zeroed pose: