A novel multiband dual-polarized reflective polarizer is demonstrated in this article, which performs dual-operation like linear-cross and linear-circular conversions in the THz regime. The unitcell consists of a thin gold film coated modified circular rings-based Frequency Selective Surface (FSS) on top of a polyamide substrate grounded with a gold film to make the reflective design. Under normal incidence, the design performs the linear-cross conversion from 0.62-0.65 THz, 0.98-1.10 THz, and 1.74-1.80 THz, with a 90% minimum Polarization Conversion Ratio (PCR), respectively. In addition, it also demonstrates linear to circular conversion with Axial Ratio (= 3dB) from 0.58-0.59 THz, 0.69-0.90 THz, 1.18-1.67 THz, and 1.87-1.90THz. Multiple plasmonic resonances are the reason behind these conversions, which are visualized with surface current distribution analysis. The device performance is stable for Transverse Electric (TE) and Transverse Magnetic (TM) incidences up to 45°. The proposed converter's dual-polarized linear-cross and linear-circular conversion influence real-time THz applications significantly. © 2022 IEEE.