In this paper, we present a new simulator called pRediCS for the calculation of electromagnetic scattering and radar cross-section (RCS) from electrically large and complex targets. The simulator utilizes the geometric optics (GO) theory and launching of electromagnetic rays for tracing and calculating the electric field values as the electromagnetic waves bounce around the target. The physical optics (PO) theory is also exploited to calculate the final scattered electric field by calculating the far-field PO integration along the observation direction. The simulator is first tested with known objects of canonical shapes, whose analytical solutions are available in the literature. Next, our implemented GO-PO type algorithm is validated by simulating the benchmark targets that have been well studied and documented by various studies. Finally, the RCS computation from complex and electrically large objects is calculated. By utilizing the RCS values for different frequencies and aspects, a successful inverse synthetic aperture radar image of the target with fast simulation time is achieved.