In this talk I will discuss some of the many fascinating and highly unusual impurity aspects of iron-based superconductors. This includes, for example, the induction of impurity-induced long-range ordered phases due to unconventional RKKY exchange couplings that would not be present without the disorder. I will also discuss disorder effects in the nematic phase above the transition temperature to the (pi, 0) magnetic state but below the orthorhombic structural transition. The anisotropic spin fluctuations in this region can be frozen by disorder, to create elongated magnetic droplets whose anisotropy grows as the magnetic transition is approached. Such states act as strong anisotropic defect potentials that scatter with much higher probability perpendicular to their length than parallel, although the actual crystal symmetry breaking is tiny. From the calculated scattering potentials, relaxation rates, and conductivity in this region we conclude that such emergent defect states are essential for the transport anisotropy observed in experiments. Below the SDW transition the nematogens freeze into dimer states that show many characteristics in agreement with STM measurements.